I'd put Exar as a SI. He has a little bit of both AC's. I wouldn't put him as a Marauder.
Especially if you follow the SI story, the first chapter goes about finding trinkets that give you power. Exar used allot of trinkets to give him power. And You see allot of Holocrons.
True, but Exar-Kun is just as gifted with his unique saber style. I would agree that he leans more to the inquisitor side.