I don't think that our special forces, who are operating behind lines in Iraq, wear uniforms or openly show their weapons. They are not such fools! The use of special forces and commando tactics has long eroded the distinction between legitimate and non-legitimate combatants. In terms of the formalities of international law, you are right, but practice is different now, and that will increase in the future.
I'll bet they don't practice perfidy, either.
In any case, this may all be academic if it turns out to be an American soldier, as it seems may be the case.