I've flown with one individual that in fact was senior enough working in the hub that he did fly for a commuter, building time while still keeping his hub job. Another individual, former Army R/W Aviator, West Point Grad, was a crew bus driver for a year, and at the same time was a DC9 Captain for another carrier. Two others I've flown with were both Navy pilots, worked for a year loading airplanes.
The reality is that most, if not all had the qualifications to get the job in the first place. They just guaranteed themselves an interview by taking the nonpilot job.