The DnD Tools quote here mentions it being "a state," and thus, is that NOT a spell?Fiendish Resilience (Su): Beginning at 8th level, a warlock knows the trick of fiendish resilience. Once per day, as a free action, he can enter a state that lasts for 2 minutes. While in this state, the warlock gains fast healing 1.
At 13th level, a warlock's fiendish resilience improves. When in his fiendish resilience state, he gains fast healing 2 instead. At 18th level, a warlock's fiendish resilience improves to fast healing 5.
So...should Fiendish Resilience be dispellable?