The rules of engagement DO NOT require medics to treat enemy combatants. There is no law within the UCMJ that requires a medic to do so. Try getting shot and being faced with that decision before you talk out of your posterior cavity.
Um, incorrect. Being an ex-medic, we've been taught that the medic is obligated to treat ALL wounded (Article 3, Section 2). It is in the Geneva Conventions which we are obliged to follow and states: (2) The wounded and sick shall be collected and cared for. An impartial humanitarian body, such as the International Committee of the Red Cross, may offer its services to the Parties to the conflict.
However, there is a caveat. Special forces units are not under any such obligations. Also, there is nothing that say's the medic can't treat HIS people first.
Oh, of course nothing say's the medic can't defend himself or his patients. As an interesting note, there are many Medal of Honor reciepients that we're medics.