Oh aye ya the Fey Union bug, that's an exception to the rule for now.
But for reference, with 510 DH I'm seeing somewhere in the rough ballpark of a 5-10% direct hit rate with my nukes, but I don't get any DH heals whatsoever. The threshold to get a DH heal could be significantly higher, but I'm working on the assumption that it just doesn't count towards regular heals at all (Union bug aside).