That report relates to credit for training not experience. The CAA certainly used to regard the Vigilant as a TMG, previously they had allowed it to be counted as SEP but that ceased. Hours flown on it were certainly countable as TMG hours.
The requirements for a PPL holder to start an FI rating are 200 TT of which 150 are PIC on aeroplanes.
No,The EASA prerequisites for a FI(A) Course are 200hours as PIC of Aeroplanes or TMGs of which 150 are PIC and 30 hours on piston powered aeroplanes of which 5 are within 6 months of the pre-entry flight test.
I can see no logical reason why his experience should not count.