A friend was denied enlisting during the Korean conflict for being nearsighted...he had already become a mechanic, with 2 years training at a civilian trade school, but the army wanted him to be perfect. Another person, college graduate, was denied an officer commision for being slightly color blind. They would take him as an enlisted person, tho. He declined.
I don't know if the military is still so fussy, but if they are, some gays might be denied the opportunity to serve on trivial issues.