... use a lifesteal ability to allow ranged units to recover? That ability from Mask of Death worked on a unit that was a Missile (Splash) attacker. It just struck me as very odd.
Yes, why else would the orb ability have a projectile image and speed defined if it was only melee? It could be that Vampiric Aura is melee only, not sure about that one.
I don't think the Mask of Death lifesteal is an orb at all. But, as mentioned, it sure does work on ranged and melee units. And Vampiric Aura only works on melee units.