Heroic Poksau's passive armor reduction is stacking. I tested it with Marianos, Bounty, Smuggler, Polaris, and Pisces - all of which stack with heroic Poksau (did not try with legendary Poksau only heroic, but it could be bugged with legendary Poksau as well).

(Only with rog and war ones) Ebon armor should be in the 30s CD. However, after multiple attempts, a friend was able to proc it again and again as little as 20s by using a timer to start it when it procs, then stop it when it procs again. It's worth noting that there was a purple shield when it proced the first time, and stopped the stopwatch when I saw the armor proced again with the purple orb + blue dmg icon buff on the character.

Essentially rog and war ebon armor cooldown's are 20s, mage one is 30s. Idk if that's intended for them to have different cooldown times.