I actually think that describes him pretty well. He does "serve" the Unlife, and is possibly its most powerful servant, but he isn't doing it out of any great belief in the teachings of the Unlife, but to further his own ends and achieve his own goals. As such, he is willing to ally - at least temporarily - with anyone or anything that helps him with this. He has, at times, aided at least some of the Orders Arnak, but they are true believers and he is not, so his goals and theirs will sometimes be at odds.