As of this moment, the quest is bugged. Tried to kill him with my hunter but he completely ignored my pet and came right for me even though I had yet to fire a single shot, so there isn't any way (given my understanding of the rules for the last ten years) he would have known I was even there. After FD, he went after the pet. At about 60% health, he ignored the pet (who then came back to me, as if it was not in a fight....) and went after me again. I backed around in a circle until the FD cooldown came off and FDed again. At that point he went into evade mode. The whole encoounter had taken about 6 minutes at this point.
Some things appear to be working. Freezing Trap was actually very effective. If you have the time to sort through this randomness or have an uber plate character, Spineslicer shouldn't be a problem, assuming he won't just evade at 5% health remaining.
If you're not in one of those classes, contact your local GM to confirm that this quest is actually working or just pass it by.