I also have 2 dwarf angels in the same tank without too much problem. The bigger one does chase the smaller one sometimes, but he also chases the coris wrasse, the springer's damsel, and the clown around as well, so maybe he's just an a$$.
As for being reef safe, I never had a problem with either dwarf angels, but I guess it's something you need to watch for. I have mostly lps and soft corals, with a few leathers and a small frag of sps (birdsnest). It's also important to note that:
1. Corals can die randomly for no apparent reason (especially sps). Just because your coral is not doing well doesn't mean the angel is eating it.
2. Dwarf angel forage for food picking picking at (kissing) surfaces. This includes glass, rocks and even corals. If you see a dwarf angel picking at a coral, they are probably just picking off small scraps of food off the coral rather than eating the coral itself.