Granulation is actually a part of wound healing; the problem comes when sometimes it doesn't progress naturally to the next step in the process and instead the granulation keeps overgrowing. So, basically, this is something that any doctor who has dealt with injuries will be prepared for - it's not unique to GRS. My GP said he'd be well-equipped to take care of it for me if need be (in the end I didn't need it, but he did provide me with useful advice regarding scar tissue on the basis of his experience with plenty of patients who'd had various [non-trans] surgeries). The doctor in question would need to have a speculum and be comfortable dealing with post-op women, but that's about it.
Actual revisions, though, would probably require a GRS surgeon...