So if you damage the voodoo doll, you get damaged as well. So, likewise, healing a voodoo doll should heal you. Right?
If the Voodoo Doll is at its max health, then healing it will not heal you, to prevent angel abuse.
I'm thinking, plate armor, blessing, or anything that increases a doll's stats should also increase your max health, and maybe weapon damage if that's possible (doubt it though).