Health percentage abilities/talents normally won’t interact with armor values, however whenever you pick Martial Law at lvl 16 with Cassia, this talent will deal it’s damage after taking (positive) armor values into account. I haven’t checked negative armor values yet.
I’ve seen the bug in game and it’s reproducable in try-mode. I’ve selected both Deathwing and Greymane as opponents, since they have passive armor. In both cases, I saw the damage of Martial Law being reduced by their armor value. I’ve checked Artanis lvl 16 Giant Killer talent afterwards, to check if a change was made in the calculation of percentage health damage skills and if it included armor now, but Artanis wasn’t affected at all.
I hope I have provided enough information, but if any more information is needed, I would gladly help acquiring it!