Just like when we stay at resorts outside of Disney, and have guests visit, we have had guests in Disney resorts, including the pool. We OK'd it at the desk, and with the lifeguard, and they have always said sure, no problem.
Our guests lived in Florida and weren't staying at Disney. We left their names at the front desk, although when they came, they just had to give our name to the guard, and mention they were visiting.
Our grands think the pools at the Stars are fun...especially the "quiet" baseball pool at Sports. It squirts water at you...as does the main pool at music. They preferred them to the POR pool, when we stayed there...even though the Stars doesn't have a slide.