I would certainly not mind having Halsin in party, after all he allready travel with us ... it would make much more sense to be if he would be willing to actively participate, than just standing in the camp, waiting for us to report what we discovered. :-/
But even if that wouldnt be an option (wich would also be huge missed opourtunity, and im quite sure lots of people would be quite disapointed, if not mad) ...
Groove is in my honest opinion prefect place for hiring Mercenaries!
Aradin and his whole group are exactly that ... some Tieflings seems to have fighting spirit and may be willing to join us after we secure the passage for the rest ... and some druids might be persuated to help us aswell, to name few, Nettie, Rath, maybe redeemed Kagha?
//Edit:
he can cast Hex which makes my Bard's spells more effective
Unless i remember something incorectly, im affraid that is not how Hex is suppose to work ...
It should only enpowers caster spells.
Wylls Hex = Wylls damage.

So if anything else happened, either i remember something wrong, or it was bug.