Not all pirate crews appoint or have people on their crew as this profession but if they want to become a really large crew and the captain will not have time themselves to recruit, the scout would take care of all of that business.
Jobs of the Scouts
In more detail, the scout is the one who goes around recruiting potential pirates to join their captain's crew. Usually the scout's are off doing other business elsewhere without their crew because there would be no other way to recruit rookie pirates into their crew. Scouts throughout Hedgehog Piece have to be a strong member to their crew because if they are to be alone traveling they have to handle any problem that is thrown at them without the help of their other crewmates and usually if you're powerful yourself you can see the potential strength others have in themselves in which you would either help to bring out or train to become better. Not only do they handle the jobs of recruitment, they also handle the job of training those recruits alongside the First and Second Mates. Usually if recruiting outside of the area their crew is in and alone, they will take the recruits to an island for various training sessions before returning to the ship of the crew. There the recruits would become honorary members of the ship and do as the captain, first mate, and second mate tell them to do.