Mechanim with AI Soldier Agents

Hi all, I'm working on creating an Behaviour Tree based AI system for a University Honour project and I'm onto the models / animation state now and I was wandering if I could have a little help.

I would like tips on which would be the best set up for adding weapon animations to the Soldier Agents. I've used Mechanim for the Civilian and Zombie agents and I was wandering how best to handle this situation.

I have soldiers that can shoot, pick up ammo, and throw grenades so those are probably the 3 main Mechanim States which I was will in conjunction with the Movement/Idle state, but I was wandering how what would be the best way to handle the animations for the weapons as the soldiers have the ability to pick up weapons off of the ground.

Would an OverrideController be best (have one on each weapon that the soldier uses) or is it possible/easier to use an IK rig and use script to change the position of the soldiers hands?