True that it does say hit; though I would argue the hero is inside the cube and the cube is what is being hit. If bullet procs are also on hit and not necessarily on damage, these do NOT apply within the cube so there is still an issue somewhere
Unsure if this is actually an intended feature or not, but currently Apollo heals on stabbing Viscous' cube every single stab as if he were hitting the player. Additionally, while I have not tested this since I do recall as well that Bebop bomb also still provides a stack when hitting a player...