Not necessarily, as they may still fight. Depending on the fish sometimes it's best to add them at different time, with the more aggressive one being added last. Adding them together may let them settle in without any problem, as neither has a Territory in the tank to fight over. At this point if they're not chasing after each other, or attack each other, then they'll probably be OK. There will always be some fighting, as long as it's not to the point where one is killing the other.