I agree with Void. I always thought of him as some sort of mouthpiece. He could walk around with some authority, and he obviously had control over the soldiers ("There's SAND on my boots!"), but I never thought of him having an official rank.

Now that I think about it, he WAS probably just a civillian that underwent the Magitek experiment. Once he turned crazy, Gestahl probably wanted to keep him close. You wouldn't want a dangerous maniac running around in your empire, would you?