He does good character writing. But when writing narrative sequences or tying together multiple storylines I have not been as enamored as many. And the romance content that is now irrevocably tied to his work (whether he likes it or not) is silly to me. Wasteful, even.
And I don't think he and Chris would balance each other out... they would either compromise each other's best qualities to the point of mediocrity or they would wind up mortal enemies and kill each other in an Old West showdown at noon. Either way, the game they'd be working on wouldn't be worth a hill of beans.
Avellone is really preachy as a writer, at least when it comes to his particular philosophy. He does it on a number of occasions in POE, and Kreia was just his vehicle to express his view on Star Wars. He's quite a clever writer mind you, and he's great with prose and nontraditional modes of speech, but I think he's really stuck in his ways and not always in a good way. I just can't see him coexisting with DG on any product but what do I know.
Plus DG just writes stuff so differently. I don't think their style would mesh at all, ignoring the fact that they seem to have wholly different philosophies on what makes for good character writing.