Are the risks for BBL lower if not much fat is being grafted?

Honestly, most healthy patients will do well with the procedure.  The best decision you can make is the choice of surgeon.I have performed hundreds of these BBL procedures and never had serious injury or major complication.  It is possible get a fatal pulmonary embolus or a fat embolus.  It is also possible to have lidocaine toxicity or puncture an internal organ.  The risk of all of these is much less than 1%. Fluid collections can be managed and rarely cause long term problems. I have not had bleeding or infection issues.The risk for complications increases with previous surgeries, higher BMIs, and larger volume extractions and fat transfers.The most common dissatisfaction relates to the amount liposuctioned and the amount transferred.  As expected, these are the 2 main reasons why Brazilian buttlift revisions are performed.  Kenneth Hughes, MD, Board Certified Plastic SurgeonLos Angeles, CAOW MORE

Your surgeon may be very skilled even though he's not board certified (yet?). However, more importantly, please read the details below regarding the risks and benefits of BBL relative to buttock implants for buttock augmentation. 
Of the approximately 20 new buttock implant consultations per week, at the very least 4 - 5 are because the results of their BBL melted away within 10 to 16 months after surgery. Hence, a combination of sculpting your waistline with liposuction and augmenting your buttock with implants provides the best chance for a long lasting and sexy "hour-glass" figure. Please read on for more surgical details:

There are currently only two acceptable surgical options for augmenting and enhancing the buttock/hip area: 1) Brazilian Butt Lift (aka BBL) - utilizing the patients own fat from liposuction then transferring it into the buttock and/or hips and 2) Buttock and Hip Implants (soft silicone rubber implants that cannot rupture &/or leak). Both are options but what it comes down to, like any surgery, is proper patient selection and long-term results. 
Unfortunately, because ~80+ % of the fat transferred will melt away within a year, most patients are not good candidates because they lack an adequate amount of fat to harvest. Beware, if a surgeon asks you to purposely gain weight (i.e. fat) before BBL, know that the fat you lose first as you get back to your baseline weight after surgery is that very same fat that was transferred into your buttock, hence your new buttock shrinks first, fast, and the most...so don't fall victim to this recommendation. Even those patients that had adequate amounts of fat pre-operatively, still end up seeking buttock implants after a year or so because most of the fat transferred melted away leaving them with minimal result. 
 Although overall using your own fat is relatively safe, it not infrequently melts away unevenly leaving one butt cheek bigger than the other or with dimpling or hard fat cysts.  The one serious complication that can rarely (< 1%) happen is "fat embolism" in which some of the fat gets into the blood stream and travels up into the lungs, heart, and/or brain causing serious problems. This complication is more likely to happen with the larger amount of fat being transferred. This is even more likely to happen when using fillers like liquid silicone, PMMA, Sculptra, and hyaluronic acids. Also fillers, when injected in large quantities, have a relatively high infection rate, guaranteed tendency to migrate away from the original area they were injected, and almost always stimulate a lot of inflammation with a subsequent and disastrous amount of scar tissue/hardening.
Thus buttock/hip implants are a relatively very good, safe, and long term reliable option for most patients seeking buttock/hip augmentation.  Contrary to nieve claims by many other plastic surgeons, intended to scare patients away from buttock implants, my overall complication rate is only ~5%.

Thank you for your question. Every type of surgery has associated risks and complications. I perform multiple Brazilian butt lifts every week, and the complication rates are very low. Overall, the procedure is safe and effective. Please do your research and find a board certified plastic surgeon with many years of experience. There are many different boards out there, but the only plastic surgery board recognized by the American Board of Medical Specialties (ABMS) is the American Board of Plastic Surgery (ABPS). Certification by the ABPS is a rigorous process consisting of a mandatory of 3 years of training in plastic surgery, oral and written examinations, & peer reviews for safety and ethical standards.Membership in the prestigious American Society of Plastic Surgeons (ASPS) and the American Society of Aesthetic Plastic Surgery (ASAPS) are two more indicators that a surgeon is in good standing and upholds the high standards for patient care and continuing educations demanded by these societies. The websites for the ABPS, ASPS and the ASAPS are great places to start. Not only can you find great information on procedures but they all have tools to determine if a surgeon is certified.Hope this helps,Dr. Newall 

There are potential minor and major complications with every surgery.  On the face of it, BBL is a relatively simple surgery.  One harvests fat from one or more parts of the body and depending on who you believe, they do some kind of hocus focus treatment of that fat, and put it in the buttocks either in the fat layer or upper muscular area, but never in the lower muscular area.  Actually it sounds kind of simple, but as always, the devil is in the detail.  How one stabilizes the fat and increases the possibility of survival in a new environment, where on the buttocks the fat is placed, what technique for placement, and what one does afterwards to increase the percentage of fat take (% of fat that stays alive in its new recipient area) all has something to do with the final appearance of one's newly augmented buttocks.  As you can see, there is a whole lot more involved in a BBL than what would be apparent immediately. Someone who has done 100 BBL's in 2 years has a reasonable amount of experience depending on how well this individual learned from his or her successes or mistakes.   Also, I think having copped to only having done 100 BBLs in 2 years makes me think your potential plastic surgeon is an honest person.  Anyone who claims a whole lot more than that with a busy plastic surgery practice either lives in Miami or is less than forthcoming.  I'm sure there are non Board Certified plastic surgeons out there who do great BBLs, and conversely (and unfortunately) some Board Certified plastic surgeons that don't do great BBLs.  However, I think you are right to be concerned that the surgeon you have chosen is not Board Certified in plastic surgery.  Certification in plastic surgery does not guarantee artistic ability.  Unfortunately, it doesn't guarantee even technical skill.  However, you have the greatest chance of safety with any given procedure if the person doing the surgery is Board Certified.All that mumbo jumbo above means that the BBL is starting to become a truly aesthetically appealing and long lasting body contouring procedure, and if you were my sister in law back in Detroit, I would highly recommend you start out with vetting only Board Certified plastic surgeons for safety's sake.

Generally speaking a Brazilian butt lift is a very safe procedure. The complications are not volume related. The most common complications are swelling and bruising which resolve over the first month. Also, you can expect to lose 30 to 50% of the fat injected. If the fat is not correctly injected some of it can die and you may feel lumps, this is called fatty necrosis. This depends on the surgeon's technique and can be completely avoided. The most dreaded complication is a fat embolism which occurs in less than .1% of the cases. This convocation can be completely avoided by your surgeon by not injecting into the muscle layer and using a large blunt cannula. #StayBeautiful @RealDrWorldWide