Having spent over 2 years on the IHTU at Daedalus I can confirm that Captains were all pilots from FAA, Army Air Corps and RAF. Navigators were PO seaman branch navs, not FAA. Techs were a mix of aircraft techs and maintainers from all three services.
On the Army's 200 Hovercraft Squadron at Browndown the CO and a few pilots were RCT (Royal Corps of Transport) officers. The majority of the pilots were known as drivers and were in fact RCT Senior NCO ex-HGV1 truck drivers. Technicians on 200 Squadron were all REME aircraft technicians.
When the units were disbanded, all officers were granted a civil Hovercraft Captains license whilst none of the NCO pilots were afforded that honour.