I recruited Da Warlord's Boyz, which obviously are a regiment of renown unit with armor sundering on their melee attack. I then leveled up and took the Drippin' Tips upgrade, thinking I'd then get poison attacks on top of that armor sundering. Well it turns out the armor sundering went away on the unit card, replaced by poison, but stayed in the unit description. I tested it out in battle, and sure enough, they will poison a unit, but not apply armor sundering.
Note: I am using the current hunter_beta.