Hi,
basically, as was previously stated, no large angels are reef safe, the closest is probably the majestic angel (E. narvarchus). To be honest, pygmy angels are not always reef safe either, but I have a beautiful flame in my reef anyway, and he hasn't caused any problems as of yet.
Regal Angelfish have a reputation for being extremely difficult to keep, and even if you get them eating they often wither and die in a short period of time. Of course, there are exceptions, but to me the mortality rate is too high to justify keeping one, and these fish should be left on the reef, along with things like Moorish Idols, Goniopora, etc.
Also, large angels get very big, often over a foot in length, and consequently need a very large tank, 150 gal minimum IMO. I kept an emperor for years in a FOWLR, they are a beautiful fish, but I would not keep another one. I may try a small majestic in my reef at some stage, though.
REgards,
Tom