I've tested this both in Act 6 and the new event quest (top path in 2.2, first champ is Quake). While away from the defender, I still degenerate, even though Hulk's ability clearly states he should regen with no exceptions.

If it is passive, Hulk (Rag) MUST regenerate. There are no heal block nodes on this path, so there is zero reason.
I figure it's a bug.