I was thinking that the traitors would be classified as Grunts, meaning they would have the alien ranks of Grunt Soldier, Grunt Engineer, Grunt Medic, Grunt Navigator, Grunt Leader, and Grunt Commander. Grunts have similar statlines to X-COM soldiers and Grunt Commanders also have Psionic Powers. Their terror unit is the Juggernaut, a traitor human in a mighty warsuit with extreme health and heavy armor. The Grunts will have the sprite of those soldier in white/grey uniforms. Deceased Grunt will become Grunt Corpse.
Partial Interrogation Research of Grunt: Human soldiers fighting for the aliens have been referred to as Grunts by X-Com operatives. Well trained and disciplined roughly to X-Com standards and armed with alien weaponry, these traitorous soldiers generally originate from countries that have signed formal alliances with the alien forces. They also come from the "scum of society", whether it be criminals, discontents, extremists, etc. Whether it is by mind control or willful obedience these troops follow the aliens' orders without question, even if it means murdering defenseless civilians in terror attacks. Even their commanders are trained in psionic arts to confuse or control their enemies. Their associated terror unit is the Juggernaut, a Grunt in a mighty and durable warsuit.