Are custom wrap around chin/jaw implants as safe as chin implants?

You require different incisions for a more complete augmentation, but the key is not this issue but the goal you want to achieve. An isolated chin implant can not equate to proper jawline blended augmentation. 

 Hi, not even close.  While placement of a silastic chin implant can be performed through a small curved incision under the chin and the jaw line augmented using a dermal filler....the same can not be said about jaw implants.  The degree of invasiveness and unwanted side effects associated with jaw implants is far greater than chin implant surgery. I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  When the chin is weak, this creates an imbalance making the nose appear larger, the mid face top heavy, the lower face looks short, de-emphasizes the lips and allows early formation of a "double chin".  
 Proper placement of a silastic chin implant adds forward projection to the chin thereby creating harmony and balance to the lower face.  Using the same incision, liposuction can be performed to reduce the fat and further shape the neck.  Excess skin, from below the chin, can also be removed through the same incision.  
 I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty (requires extensive tissue dissection, bone cuts and placement of metal screws and plates to secure the cut segments of bone).  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone.  
Hope this helps.