Tank Brann just stands there in Underkeep while you are attacking the black blood canisters slowly as a healer, he only engages in the fight when the black blood ooze mobs spawn from them.
He also ignores the spreader hatcheries while you attack them in Earthcrawl Mines.
Edit: seems like he does not attack the containers as healer, either, but does drop potions since I’m in combat. I’m guessing he would also do this as DPS, but haven’t tested.