I believe so, that you will take double damage from a physical aoe. The only evidence I can think of is when I'd use cover on a player being marked for shiva's beam attack in ex mode, and then get hit by the beam myself as well, I'd go flying, hard, clear across the ring as if I were hit twice (pretty hilarious actually xD). I assume the damage is counted twice as well, but cant say Im 100% certain. Im a little curious also actually but on a practical level, dont think there are any physical aoe's that get regular use in pvp

Another thing about stuns, the resistance timer resets exactly 60 seconds after the last non-resisted stun. Meaning if a pld stuns the healer twice, but then decides a third one isnt worth it, and a monk shoulder tackles them 59 seconds later, they're going to have full resist for another minute after. More importantly, the pld probably loses the ability to track resistance and is left guessing when they can do their stun locking again.