Until the events leading up to the game, though, sourcerers were the good guys (at least in recent history), fighting with and in the Divine Order against the Black Ring. It was only after the Black Ring was defeated and the Divine One absent (Rift Running; see the Beyond Divinity novella) that there was a change in leadership within the Divine Order and sourcery declared illegal. Even with sourcery having a history of being forbidden and seen as corrupt / dangerous, there would be some sympathy and support for sourcerers.

Not all soldiers for hire would care about the moral position of potential employers. If a job involves going against the Divine Order (which some might be inclined to do anyway, even if not being particularly sympathetic to sourcerers), it would just need a payoff corresponding to the danger.