Actually I bet it would bring up their stats in alot of cases. All the people with lower numbers who get accepted would like to go there, but the people with high numbers that got in there and into a better school would not go to the better school.
Look, being gay is a choice. You do not choose to be black or white, but you do choose what gender you like to do. If gays are an URM then someone could claim that white males who like little boys are a URM also. If you can choose it, you cant use it.