I have a male and female blue damsel in my 55 now. I have several gobies and a pj cardinal in there also and they all get along. The only problem i had was when i put a firefish in there.....WOW. Oil and water there. It looked like a payper view smackdown. My only advice; don't put a firefish in there with the blue damsels, the firefish will loose that fight.
I have a lawnmower blenny in with a blue damsel that is very agressive. The lawnmower ignores everyone - been together about 2 months.
The only thing with the lawnmower is that I grow algae in a fishbowl in the laundry room (yeah, I grow it!) now that he has mowed down any resemblance of it in the display tank. He won't touch nori and I don't think he eats the spirulina, so I make sure he's fed.
I put some rubble in a 2 gallon fishbowl in a sunny window with an air pump and drop an "algae rock" in the display every couple of days to make sure he gets food.
