Well the only race I can see on frowning on gays is vulcans.
Im still trying to see how in the ENT novels when they mentioned a gay vulcan it works. I think that a example of inappropriate shoehorning.
Its not logical. There is no practical benfit unlike hetero relationships which bare children. And choicing ones mate based on attraction is a emotional idea not suited to a true vulcans.
I doubt they would actively discriminate against a vulcan if they did choose that path, but it would likely not go further than tolerating as they would view that vulcan as being emotional.
Even interspecies male/female seem to be a exception rather than a rule with spock being slightly looked down upon with his half human side by other vulcans.
Of course when it comes to other species and what they do i doubt they would care as we are just emotional and illogical by nature.
This would hinge on the evolutionary benefit - simply going on lack of offspring doesn't rule out an evolutionary reason for the continuation of homosexuality in a species. We see that all around the place in the animal kingdom and modern science has many a hypothesis that attempts to explain why.