All our technical ground instructors are type-rated company pilots (the vast majority of which are captains) who fly on the line. They aren't necessarily training captains, although some are.
Although the initial type rating groundschool is predominantly systems training, I think it would be unusual to have it taught by someone who'd never flown or used the systems on type. I suspect a lot of experienced students (who ask the in-depth questions!) wouldn't appreciate a non-TR, non-pilot as their instructor. Not sure what the regulators say about experience requirements though...
Plus, TR courses aren't regular enough to provide
enough work for someone on the company payroll who only does grounschool duties. It may be different at third-party TRTOs...