IMO I do NOT think that sexuality should be discussed or disclosed on anyone's application. Personally, I really despise labels of any kind, and despise the whole "LGBT..." branding. The whole point of LGBT activism is to show the world that LGBT people are all "equal" which they are. Basically, all human beings have a right to exist in liberty, peace, and happiness and differences between people (sexual orientation, gender, religion, ethnicity) should bear no impact whatsoever on someone's ability to contribute to society and lead a meaningful and purposeful life. In my opinion, up to the point of face to face interviews, all applicants should be a "code" only, with all individual characteristics unknown. If it so happens that interview time, all applicants are female or all straight or all black, well then it must be that these people had the best marks/scores/life experiences/application letters to warrant an interview.
Unless you happen to be the president of your school's GSA or a co-ordinator of your local pride event or write a long letter about your religious organizations mission to some foreign country, there should be no other proclamation of your supposed religious / ethnic beliefs or your sexual orientation.
I think that is the only way to achieve a fair society. Show you belong on the basis of merit and character, I'm 100% open minded to all human beings who show respect towards others, and carry themselves in a mature and professional manner. Like I said, if it is all based on merit and the entire class turns out all gay, or all female, or all black, then that is the fairness of the system.