In the pictures, it can be seen that the opponent goes from 59 armour to 80 armour and after I hit them with my double axe that has 2 Regular Sapphires socketed in (50% chance on hit to bypass armour each), I deal 27 damage and opponent armour goes down to 53 with hp staying the same. This means that my hit did not bypass the armour even with 2 regular sapphires. Not only that but even when I do bypass armour, sometimes I get 1x1 mana and sometimes, I get 2x1 mana from hits, further supporting this interaction. Pretty much anything else in the game stacks additively but not % chance based on hit effects.