Yup, amphipod. (More than likely of the Gammaridae family)
Some consider them good guys, as they eat detritus and micro algae.
Others with no fish to eat them consider them a nuisance. In large quantities, they can annoy corals when they crawl all over them.
As long as you have some form of a predator (damsel, wrasse, hawkfish, etc.) they will keep numbers in check and supply a nice little snack for the fish.
Thanks for your quick replies. I bought a small rock with some zoas from a local hobbyist and I did a Red Sea DipX (as I always do with new coral) and there were at least a dozen of them of various sizes dead in the dish. I feel better knowing if some didn't get removed it wouldn't be a crisis.