I do not think a ones sexual orientation is "any more or less likely to be emotionally or physically disqualified from cohesively serving"
I will caution, that men typically behave differently when in the presence of a woman, or a homosexual male.
Think of a few mechanics working on a car, what happens when a girl walk into room?
I will also bring to light, even though I was able to make it though bootcamp, It was very awkward having to showering with people who were attractive. I can see how it would be awkward for them, if they knew i was gay, and i was soaping up right next to them, but bootcamp was filled with awkward situations. I don't think one is fit to go into battle, if your too scared some guy might be checking you out in the shower.
I believe our troops are smart enough that, even those with a long stand bias against gays, are capable integrating.
I'm sure that there has been a gay baseball player at some point, To my knowledge, no one has ever come out while while playing baseball... because....? I think he does not wish to cause controversy in the club house. In this day in age, I don't think most of the clubhouse would care at all.