If it's an issue, dealing in broad nationality strokes, I'd actually suspect the Earth Kingdom and the Fire Nation to have the hardest issues (based on their history, mind). The Water Tribes, being adaptive by nature and being not too far removed from arranged marriages, would probably have some issue. The Air Nomads/Acolytes would be the nation without an issue.

That said, that's if there's an issue of anti-gay bigotry in Avatarworld. It's just as possible that there isn't one at all, based on what we've seen and that they're analogs for cultures that didn't originate that specific bigotry themselves.