Culturally speaking, you're not going to see something remotely related to what you're talking about in any official merchandise. I'm not even sure why this topic is set up as a poll, but that's just me.
If you want to be somewhat realistic—which would involve assuming Pokemon are realistic despite all their impossibilities—then yes, they can be as homosexual as any other documented sentient organism on this planet.
As for Attract/Cute Charm, as mentioned by GhastlyCare, it's heteronormativity. That's the result of culture. Millenia of culture. It's always been that way. Now I'm completely tolerant of any sexual orientation and I'll do my best to avoid any hints of discrimination and otherwise, but for the sake of this particular point, male-female combinations are traditional and the norm. And well, for the sake of a species' survival as a whole, that's kind of how it is.