The yellow tang would hold his own better than the mimic tang. The mimic tang is a very mellow fish and can be sort of hard to keep. they need to feed all day. if you were to try either, my advice would be to get one much (so he is not a threat) smaller than either of the other tangs or larger. Just dont get one around the same size. Last get a critter cage and drill tons of holes. Keep the new fish in the tank with the critter cage for 2-3 days and see how the other tangs react. If they keep going after the fish in the cage, you might want to reconsider but chances after 2 days they wont think twice about him.