From what I understand, yes it is covered. You just have to provide them with documentation which your surgeon would already be requiring you to get anyway - 2 letters from mental health professionals, and a letter from the doctor supervising your HRT. I'm unsure if there are any other Medicare/Medicaid specific requirements. If there are, it's probably just internal paperwork that they can get to you.
The one thing that's sort of limiting with using any kind of insurance or Medicare/Medicaid is that you can only go to surgeons that accept that. Your best bet would be to look into surgeons working out of university hospitals. Most of them seem to have agreements with Medicare. Off the top of my head, you could look into: Dr. Berli & Dr. Dugi at OHSU, Dr. Salgado at the University of Miami, Dr. Kuzon at the University of Michigan, and Dr. Bluebond-Langner and Dr. Zhao at NYU.
If you have your heart set on a particular surgeon, you could always call and ask what they accept.
I don't know if you're on Facebook, but I believe there is a group there specifically for trans folks seeking to use Medicare/Medicaid for surgical coverage.