What are the risks with having a tummy tuck? I have pelvic congestion syndrome

It is not clear if varicose veins are likely to cause DVT, but the two conditioners are certainly related. 
A number of factors (genetics, age, obesity, birth control pills, hormone replacement therapy, occupations that require a lot of standing) predispose an individual to PCS. You will need clearance from your vascular surgeon to have a TT as increased pressure in the abdomen or trauma to the area may be cause for concern so that precautions can be taken by your PS.

I have never heard of pelvic congestion syndrome. However you can always have a tummy tuck with no muscle tightening. This may avoid any issues with internal organs. 

Depending on the size of your varicose veins it may cause a slightly greater risk of bruising, bleeding, and hematoma formation but a frank discussion between your plastic surgeon and vascular/varicose vein surgeon needs to be had to ensure your safety and to minimize complication risk. 

Dear newmomnewerbody,
as long as you get a clearance from your doctor, you might be a candidate for a tummy tuck. If you are considering a surgery, I would suggest you to consult a board-certified plastic surgeon. Only after a thorough examination you will get more information and recommendations.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

As it appears your condition is well controlled you still may be a candidate for a tummy tuck.  You will want to speak with your vascular surgeon about your desire for a tummy tuck.  If given clearance you can then proceed in scheduling a consultation with a board certified plastic surgeon.  

I recommend that you address this with your vascular physician but, if you are largely asymptomatic, it would likely not contraindicate abdominoplasty but would require clearance from and consultation with your physician.