Everywhere you look cautions you not to do it. It would be a pretty costly mistake if something were to happen. I ha a coral beauty and a cherub and it was a constant game of cat and mouse with a very undesirable outcome.
The Key is to get them small and add them at the same time. That way they will discover your tank and claim a section for themselves. I have 3 carib flamebacks in my 150 and not once did anyone give me trouble.