I have the 2010 Hellbents and I find the groomers to be just fine. Granted, I don't ski groomers on my Hellbents often, and you won't be laying down any beautiful GS turns on them. But they will take you down a groomer none the less, they will just feel like a wider, bulkier, ski.
In addition, K2 change the design of the Hellbent starting with the 2011 model. They made them a little fatter under foot and added a tiny bit of traditional camber under foot, so the 2011's onward probably ski even better than mine, at least on groomers.