i say if anyone wants to serve, and has the capability to serve in the military they should serve. whether the that person is straight, gay, bi, or anything else that comes to it. the orientation does not determine the capability as a soldier, its the personality. I have met bad and good soldiers of all orientations in my time in the army.
To this day i still find it funny the excuse some of the politicians used the excuse that straight male soldiers will find it uncomfortable during guard duty if they share a guard tower with a gay soldier, because the gay soldier might see the straight soldier as a sexual object. Yet it was policy of the army that if a female soldier is on guard duty, a male soldier has to accompany her at all times. I'm sure neither one of them wont see the other as a sexual object in that same situation.
The way i see it, as long as the person performs his job with the skill and dedication of a soldier, i dont care what that person does during his off time.