The Watchtower Personnel helped the Justice League maintain the second Watchtower. Among them were medics, mechanics, teleporter operators and many other highly talented individuals with various job positions. They were transported to and from the space station from a rural location in relative secrecy.
On one occasion, the Task Force X posed as Watchtower Personnel to infiltrate the Watchtower and steal the Annihilator. They were able to get into the Watchtower by working with an "inside" Watchtower personnel member.
The concept of personnel on the Watchtower took time to develop. With Justice League Unlimited they became a permanent fixture, but how they were hired, who paid them, and their training was never covered in any great detail, although the episode Task Force X focused on them much more than most episodes in the past.