Although I can't speak about compatibility with your existing fish because I don't know, we got a Diadem Dottyback. A small fish only about 2 and an half inches long and he's brilliantly colored with a vivid purple back and bright yellow body.
And an enjoyable fish too as he's usually quite "busy" ... checking things out (He'll look right back at you as you gaze into the tank), zipping in and out of the smaller passageways through the rocks, popping his head out to see what's going on.
I believe dotties in general can be a bit pugnacious, but I understand Diadems to be one of the milder of the type. Ours hasn't caused any problems with our Oci clowns, BG Chromis, YT, or skunk cleaner, although he is certainly not bashful and doesn't shy away, even from the tang which is about 20 times his size. The worst things he's done is "stolen" our skunk's favorite spot, claiming the area and forcing the shrimp to find new digs.
