OK, what exactly is so "gay" about an incubus? It's basically just a male succubus. They're bat-winged demons who torment mortals, only they tend to prey on mortal women instead of men like the succubi perfer. I fail to see what's so gay about that, unless we just have a classic case of sexism going on here...
Anyways I think it would fit fine in Castlevania. It's true most of the main characters tend to be male, but we're starting to get some playable female heroines such as Maria, Charolette, and Shanoa. I could see an incubus villain trying to tempt one of them just like Magnus did Maria in Nocturne of Recollection.