I have had a copperband in my reef with 6 clams (2 Maximas, 2 Croceas, a Derasa and a Squasmosa) for 2 months. The copperband seems to behave itself well. You can't have featherdusters in the tank though with a copperband.
FWIW, Nathan
Disclaimer: Fish behave much like people. Often very unpredicatably!
I kept a copperband with clams with no problems. With their mouth structure, I doubt that they would tend to bother clams. As npaden mentioned, they are guaranteed to pretty much wipe out all feather dusters and they can be extremely picky eaters. One of my favorite fish for thier looks.
I've had my copperband in my 180 since last December. It is in with 4 clams. Two crocea's, a maxima and a squamosa. never has even looked at them. My copperband hasn't touched any of the sps either. It loves mysis shrimp though. HTH..