Grenadier plus the Tinkerer version of grenades should net 9 hatred per casting of grenade. The bat companion is good for another 2.5hatred/sec. Combined with the extra hatred pool from Vengeance and hatred from health globes, it should be fast to fill up on hatred.
Aside from that, there's the rocket version of Cluster arrow for large groups. Multishot would probably work just as well, but after taking the Grenadier passive it seemed to make sense to use cluster arrow.
Rapid shot with rockets is there for single target takedowns and small groups. 228% base damage plus 4 rockets at 70% weapon damage each per second is 508% damage per second on one target (as long as it doesn't have any friends around) for about 10 hatred a second. We'll see if it actually works like that.
Strafe is useful for when standing still is not a good idea.
The sentry is there to do some damage with the discipline that otherwise is being used for much, and more importantly, it shoots more rockets.
I could see dropping the companion for marked for death or maybe shadow power. It also doesn't have any defensive skills. However, I could see this being a blast to play.