If you really die die want to get dwarf angels you will first need to train them to feed on pellets. Once they are pellet trained chances of them nipping on corals are slim, one advice Eibli angels are very prone to nip at corals even if its pellet trained. That's from my experience with Eibli, but so far the angels that i am keeping are not nipping on my mushrooms, zoa and clams.
Angles that i have now are Flame, Flame back, Multi coloured, Blue face and Coral Beauty.
Hope this helps. Other reefers might have different experience so lets hear from them 1st before you commit.