Look at his buffs next time you run it. Here's a hint:
Me and my fiancee ran into the same issue with Snipe last night when we did this place. He just hung back and spammed 3k damage hits over and over. She (sith sorc, full healing spec) could not heal the damage.
Couldn't tell if whether he used it or not was linked to the adds being up at the time, my suspicion is that the adds need to die quick and then he just stops using it. If this is the case then it's just a simple matter of focus firing the adds down quickly, even saving cooldowns to take them out. We were 3 manning with my Vette and a 34 sorc DPS spec, so that could have been the problem.