No, CPT. rex is not an arc trooper. any internet encyclepidia
says so, and the fact that arc captains are red colored, while
captain rex is blue.
Major zeo: Actually rex is an arc trooper and all the other
commanders in the clone wars are also arc troopers. Such as Cody
and bly all the commanders in the clone wars were trained by arc
trooper alpha and they graduated the arc commander program.