Yes, it does provoke. It seems to go against the flavor of the ability, but it's been made relatively clear (it was clarified in a FAQ, and one of the Epic Feats on WotC's website for Warlocks specifically mentions that the Warlock no longer provokes AoO's on a Hideous Blow). You can always use it defensively, though- so it gives the Warlock some more incentive to beef up their Concentration.