There's plenty of homosexual behavior in stallions, and occasionally there are stallions who only seem excited about other stallions and geldings. So I'd say yeah.

I have been around a lot of horses and the males really never seemed to care what they mounted

Just about every sexually reproducing species that we have extensively studied has had some level of homosexuality pop up.

The more interesting ones are the documented cases of trans individuals. Some fish and reptiles can straight up change genders and be fertile. Birds and mammals have documented cases of females starting to exhibit male characteristics in the absence of a male.