Does Galio's shield proc Athene's Unholy Grail's passive?

its not a shield. a shield is a gray, damage absorbing bubble around your health bar.

galios bulwark is a buff.

so just to be clear, galios bulwark and athenes have no synergy.

Athene's expressly indicates that it stores up premitigation damage, which is a fancy way of saying a shield that absorbs damage for you until it hits it's limit. Galio's "shield" is a straight stat buff and in no way absorbs damage.

it would work if it healed the ally instead of galio himself.

to clarify, "shield" means an actual health shield and not a resistance buff.