Difficult to say: he's a devil. They don't trust anyone, especially mortals...
Thing is, if he doesn't grant assistance, what would you be beyond a Demon-hunting-specialist in a non-good mould? Isn't that just a Hellreaver with the mark of Avernius?
I merely quibble because this really isn't in the style of the other "Disciple" classes, which were all cult leaders of one type or another, but Bel doesn't have any cults... not to mention, this guy seems to be a war leader rather than a cultist. Heck, the 3rd, 6th and 7th level auras seem connected to other lords!
I'd call this "Champion of Bel," "Student of Bel" or "General of Avernius," simply because it doesn't really do any cult stuff and seems to have flavour from the other contingents operating on Avernus.