UHC / MEDICAID
You have double coverage. In most cases, if the primary payor (UnitedHealthcare) will not pay for the surgery, your secondary payor (Medicaid) will not pay for it either. In most cases, the secondary payor follows the rules of the primary payor, but depending on how exigent your case is, exceptions can be made.
The best thing to do is to contact Medicaid's customer support department to get explicit information on how bariatric surgery is covered in relation to your primary health insurance. If you get positive information about coverage, then you will want to request that information in writing.
I hope I was able to answer your questions appropriately.