I wouldn't quarantine a butterfly for disease, ime they are one of the hardiest fish in that area. A bare tank would be bad. But if you feel the need, just set up a tank with live rock to get it eating before introducing it into the main tank.
Aggressive fish in the main tank are sometimes more of a problem for the butterfly, but I agree, if you can get some weight on it before hand, it will likely overcome. Fish seem to accept butterflys for the most part.
