i had one before losing him to power outage. in general large angels (and most dwarf angels) are a really bad bet for a reef tank. though like what Steve said, some angels may only pick at certain types and not others, but you wouldn't know until you put them into the tank. it's an individual personality thing.
you should also keep in mind that emperor angel grows very large, 18" in the wild and you need a minimum of 8', 300 gallon tank to properly house one. when full grown their bodies can be more than 2" thick, really fat.