Does Hextech Gunblade heal passive stack with that of Will of the Ancients?

Hextech Gunblade has a unique passive which heals for a portion of damage dealt, as described in-game:

Heal for 15% of damage dealt. This is 33% as effective for Area of Effect damage.

Will of the Ancients has a very similar unique passive:

Your spells and abilities heal you for 15% of the damage dealt, calculated before you target's resistances. This effect is reduced to one third for AoE effects.

I thought that these passives seemed too similar to stack (and maybe be too overpowered if they stacked), and so checked the wiki.
Hextech Gunblade is listed as having a unique passive called Omnivore:

UNIQUE – OMNIVORE: Instantly heal for 15% of all damage dealt, including physical, magical and true damage.
Area of effect damage only heals 5% for every unit affected.

Will of the Ancients is not listed as having this named passive Omnivore, yet on the page for Omnivore, one of the items listed as having it is Will of the Ancients (and to add to the confusion more, it says "not uniquely named, but same effect" and "pending for test").

This is all rather baffling. Is there a concrete answer as to whether the Hextech Gunblade healing passive and Will of the Ancients healing passive stack?