I don't see why not.
Being gay doesn't affect your military ability in a negative way.
Infact, history has proven the opposite. See:
Theban Sacred BandThe flamboyant, annoying gay guys wouldn't be going into the military anyway, they aren't cut out for it. Just like weak straight guys aren't cut out for it.
There is no reason that any country should deny themselves a more bolstered military just because of moral belief.