HIAB on training vehicles

It sounded a simple question, but the more we thought about it, the less simple it seemed.
Are you providing a service if you use a vehicle as a base for HIAB training, the exemption for driver training is possibly not ment for HIAB training, but when the vehicle is a driver training vehicle with a HIAB fitted is it still only a driver training vehicle.
I’m not even sure how the topic even came up, but in the end we concluded that as most of the companys who do HIAB training use a driver training vehicle & are reputable, then it must be legal.