Mimic Tangs eventually turn into Chocolate Tangs which is not necessarily a bad thing.
http://www.fantasyreef.com/database....d=7&itemid=260
Everything depends on the size of your tank, the amount of rock you got which also supplies their sleeping quarters (very important - most fights happen at bed time when everyone is looking for a safe place to spend the night) and of course the temperment of each angel. There'll be a scuffle in the beginning but it should settle down after half a day or so.
My Lamarck Angel is second-in-command while the Yellow Tang is the Grand Poobah.
HTH