There is a good thread here on RC where the OP kept a running tally of members experiences with dwarf/ pygmy angels and their "safety" in reef aquariums. While it is often stated that for many species it is a 50:50 chance that they will be "safe", it turns out that most species were closer to 75-80% "safe" (i.e. not picking at or eating corals).
I have had several species of dwarf angels over the years (coral beauty, flame, Eibli's, cherubs), and none of them have ever eaten a coral or damaged one. However, I have acquaintances that have lost various corals to flames, beauty's, potter's and rusty's. It is commonly believed that keeping them well fed will reduce problems, but the rusty that caused issues was in a large 100+ gallon display and extremely well fed (i.e. fat).
Unfortunately, they is still a risk, no matter the species - to be honest, even "safe' fish can pose a problem every now and then. I once had a large female clownfish eat an open brain coral!
I currently have a small coral beauty in one of 40B's, and it has touched nothing to this point over 2+ months. I also have a mated pair of cherubs on my 50 cube with wall to wall gorgonians, flower nems, zooanthids and mushrooms, and they have touched nothing over 2+ years. I would like to keep a flame in my other 40B, but I have an open brain that I really like in the tank and don't want to risk it.