I have had a Copperband for years now, and have never had a problem with clams; however, Jan is right, they may pick al LPS, especially fleshy ones like scolymias, lobophylia and wells. Usually, if you add the fish last it will not pick at existing corals, but that is certainly not a guarantee.
They can be a bit tough to get to start eating, but they do an amazing job on aptaisia.