I dont know exactly either - I suppose because there were few if any US or UK natiionals who served with the Germans. I do know the penalty for treason is death, however. I think a drum head courtmartial should have dealt with these men.
Today, we wouldn't be able to execute those Nazi/Germans who landed off Long Island in a submarine in the forties, as we did. We were definitely at war, of course. I wonder if congress passed a declaration of war, if things would be different, but of course, GW doesn't want to go hat in hand to congress every ninety days for more money to wage war.