The "pierced armor" effect should work on Despise bosses providing your Despise creatures a damage boost from quick glance of the code.Pierce armor add 10% of all incoming damage by any player or pets to the target for 3 seconds bro :
Armor Pierce, now applies a “pierced armor” effect to the target which increases all incoming damage to the target by 10% for 3 seconds with the exception of direct damage special moves. Ranged weapons with this special move will not reset duration if target is currently under the effect.
Pub 81