To be a little more technical.
If they are wearing "uniforms" provided by the ship/laundry, then they are ship employees. (MDR, Customer Service, Room Service, Baristas, maintenance, security, etc).
If they are wearing street clothes, then they are 95% vendors: EFFY, Princess stores, "Princess" Fine Arts, guest lecturer's, guest entertainers, ONE/Future Cruise "consultants". etc.