Hi there!
Im looking at rolling an Adaar and ending up eith Bull on this run.
So my question is: can yourecruit him after youve delt with either the mages or the templars. To me it makes moresense to get a merc group in once you get get to skyhold and realized you need an army to deal with Cory.
Does he have interesting things to say on either the mage or templar quest?
Would it make it harder to get approval if I get him later in the game?
Thanks a bunch
You can recruit him after the attack on Haven. In my last playthrough I decided to wait till after Haven to recruit everyone, and the recruiting dialogue is actually quite different, with comments on Corypheus and the dragon. It was pretty exciting for me to hear new dialogue. 
I don't think there's that big a difference in how much approval you can get from him. I completed the templar quest and he did comment on it after the fact - I managed to lose some approval by teasing him about demons, which he didn't find nearly as funny as I did. Got him to like me again by judging a few people from my Skyhold throne, though.