IME, they are quite peaceful with the right mix of fish and in the right size aquarium. If they are going to show aggression, it's usually in smaller tanks and against fairly predictable fish... fish that are similarly shaped and colored (the two-toned firefish), and fish that occupy the same holes in the rocks (midas blenny). They can be kept with both in a larger aquarium but it can be a different story in that 50 breeder.
As for catching them... when I used to work in a lfs, the owner was wish washy about throwing fish in a 125 gallon display reef so I would have to get them out on occasion and had three methods. First was simply putting flake food (since it floats) and using an oversized net to get them when they came to the surface and this nabbed a couple yellow-tail damsels. Second, I would put a conch shell into the tank and wait for it to get inspected by the desired fish and plucked a Flame Angel out of there in about fifteen minutes. Finally, I just started net feeding the tanks which is just using the net to empty the thawed frozen foods into the tank. It didn't take long for the fish to recognize the net as part of their feedings and lost all fear to the point that I had to be sure that no fish were in the net when I was done feeding!
Good Luck and hopefully changing the rock work will help things out a bit, but if not, I hope at least one of these suggestions can help you out.
Mike
