might be hard to shower with cichlids in your tub =P
Pffff, bathing with your fish is a great way to make sure they stay clean, don't want them stink do you?
In all seriousness, I don't see why it wouldn't work, I would definitely make sure the tub is cleaned thoroughly. There's a pretty good chance there's soap and chemical buildup which will certainly interfere with the fish's ability to live. The other concern would be the open top, unless you were to construct something, there's always the possibility that the fish may leap for freedom.
With all that said if you're going with a bare bottom water changes would be so simple. Just drain and refill