That sounds like a way around this problem, all right... That said, it really doesn't seem that this is the way it was supposed to be done...
It's not; normally they walk up, thank you for your service, and then tell you to get lost.
Make sure you're not near the tree when the fight ends. I can't remember, but I seem to recall them getting hostile somehow and I think it might be the proximity to the tree that causes it.
The advocate is a demon. Demons in this game are Bad. If you have Lhose in your party, killing the Advocate is in fact very important for her quest. So feel free to kill him and good riddance.
It hurt me to embrace Adra at the end of the game for the achievement and give him divinity, lol.
So gross. I hate demons!