Oh Lordy, not this again.
Sexuality can be seen in both the alien and predator universes. Everything is sexualized in Alien. The original trilogy revolves around a female character being chased around by ravenous d*ck monsters. It is what it is, and so far, it's been pretty damn good.
As for predator, could there be gay predators? Could there be female predators? Absolutely, but only if there is any larger societal/sexual structure to them. All we really know from the films is that they're manly things that cruise around in big ships together, wear fishnets, have a penis cannon on their shoulders and hunt half naked muscle men in humid environments. If anyone thinks there is nothing sexual, or even slightly homosexual about any of that, brother/sister do I have news for you.
Perhaps they're asexual. Perhaps they lay eggs in some form. Perhaps there is no physical difference between male and female that would be discernable to us as humans. Maybe it's just scent based. Who knows? It doesn't matter. I wouldn't mind if there were gay or female predators. Either one would still be bad news for anything they were hunting. The issue could only arise if they were including scenes of predators getting sexual, which I feel is unnecessary and shouldn't be shown merely for the fact that it humanizes them too much.
As for gay characters in either franchise? I have no problem with it. Lope was proof positive that it can be done just fine. It's just like sexuality in any other form on screen, as long as the movie isn't going out of it's own way to constantly bring up the subject of sexual preference, where's the problem? It's simply a non-issue. I say just leave all the sex to the B-movies. This is alien and predator, it's gold star horror, and that needs to be the main point of focus in these stories.