To my best knowledge, and no testing has really been done just what sounds logical, healing power will effect any healing that comes from you personally either through spells or regen effects. Healing Received will effect any healing from an outside source or is caused by effecting something or someone else, which technically is what lifesteal is, you’re taking healing through damaging an enemy.
So as I gather you want only healing power on him unless you were to get something more from that one helix where hit someone with your poison returns health to you.