Actually, magic resistance would be a very useful thing. These are some very powerful opponents, but they mostly rely on spells to do their damage - so having someone those spells won't hit as hard, who might happen to have the majority of the phoenix down equivalents, could well be excellent. And if he'd be similarly resistant to healing spells, well, I daresay Bar could provide potions.

As far as getting Varric involved, would a setup a bit like this interest him? (Except, of course, in the bar rather than a forest miles from anywhere.)