Return of Reckoning

Question in title. For those who know the ability but not the name. It's the IB attack that gives armor to yourself and your oathfriend. Does this stack with armor pots or no?

No

It does override the pot though, for instance if you have an 800armour pot and use GA with a 900armour bonus for the 20 second duration GA will buff your armour by 900. So if you forget to keep it 100% uptime you have the pot to cover you.