Because he would just be a terrorist, like those guys at Gitmo.
Terrorists of course do not have a responsible chain of command; they do not have a justice system nor rules of engagement governing their behavior, and by definition terrorists use civilians and civilian assets as shields from which to shoot, or to prevent assets from being targetted. Terrorists do not walk around with their suicide belts visible because if they did they would be noticed and could not complete their missions. For the same reasons they do not carry identifying insignia or documents, nor do they wear uniforms setting them apart from the civilian population. They need to blend in with the civilian population in order to use the civilians for cover.
Hussein, by taking command of such terrorists, is a terrorist in his own right. He willingly chose to be an unlawful combatant, and therefore chose to discard any POW status he may have been afforded had he simply commanded his uniformed services and enforced appropriate rules of engagement.