Well, Ilha Grande is great, but it's very rustic and wild, not to mention sparsely populated, so I don't believe there is a gay spot, but I could be wrong, since I'm not gay.
But Búzios, on the other hand, has plenty of gay spots. Well, it's not thing compared to some spots in Rio where you can say some places cater almost exclusively to the gay public.
Searching the web for gay-friendly pousadas in Búzios, I could find two:

http://www.ourhousebrazil.com/
http://www.maisonduchene.com.br/