Soldier to soldier transfusions are not uncommon in a war.
Just recently a young Iraqi child was saved by walk-in blood donations from soldiers.
What would be the consequence if that child then contracted AIDS.
This is a terrible idea and consideration should be given to removing the don't ask, don't tell provision to outright denial of the ability to serve in our military in any capacity.
I would be very surprised if the military (even in emergency situations) did not routinely screen collected blood for Hepatitis B, C, HIV (multiple strains) and syphilis, as they do routinely in the Red Cross.
U.S. military personnel are required to have an AIDS/HIV test every 12 months. In practice, due to pre-deployment screenings and other unit functions, they actually get it more often than that. I'd take a blood transfusion from any soldier over any civilian; gay, straight or otherwise. No one is screened better.