It all depends on where you get your live rock from. Most people who get mantis, crabs, macroalgae, & corals get maricultured rock from companies in Florida who are licensed to place dry rock in the ocean, then pick it out at a later date. It you get it from someone's tank (other reefers or stores) you'll get whatever critters they have in their tank. If you get it from somewhere that gets it from a non-US island, there can be varying degrees of how they treat it, but they have to remove any visible life due to CITES. You can still get hitchhikers from that if they're deep in the rock. You'll mainly get hitchhikers from purchased frags.