I may be wrong here but, the way I read it, is that the driver has the capacity to govern the amount of descent braking to the van, the same as they can regulate the braking when towing on the road.
If this is the case, wouldn't the driver then set the van braking to match the descent of the tug, be it compression, tug brakes or a fancy "Descent Control" setup?
It might even be helpful in the case of a big, downhill compression lockup.
Someone may have to give one a crack.