Singapore Angels are in a unique group of angels that are very very similar to butterflies, and have similar tastes. I'm a fan of Singapore Angels and think they are a beautiful fish for a Fish Only tank, but in almost 40 years of keeping a reef have never once even thought about 'testing' a Singapore.
The Genicanthus are 100% reef safe as a group. They are open water fish that are plankton feeders, not polyp or crustacean.
I like angels and keep a bunch in my reef tanks. I've had good success for the most part with - Goldflakes, Goldens, Joculators, Interuptus, Flame Back, Venustus, Flames, Bellus and Regals.
I've had temporary success with Multi-Bar, Multi-Color, Chrysurus and Navarchus.
The amount of success you have is going to depend alot on the maturity and size of your reef tank. A mature reef tank has an abundance of natural food on it. There is lots of life for the angels to nip and pick at.
And a mature reef tank with a dense coral population has alot of places for Angels to Nip without doing damage.
Most angels will nip at a coral and move on, maybe causing only the slighest bit of damage that recovers in a day or so. But pending on the angel, and the coral, once they get a taste they may devour the coral. My Goldflakes were awesome in a densely packed SPS tank. But Acans were just something to grow out for a few months before they decimated all of them in 24 hours.
Chrysurus are good for removing Zoanthids from a reef tank - And they are smart too - They won't remove all of them, just all of your favorite and most expensive.
I have an Imperator that I have raised in an SPS frag tank for over 2 years. I moved it into a populated SPS tank and it did awesome. But Elegance Corals were just something it could not leave alone. And I worried that something that liked Elegance that much would eventually realize the hammers, bubbles, torches and frogspawn were just as tasty.
Dave B