That's certainly true, as their annually involved in the 1000m Peak Race, but over the many years that Ive driven up and down the Nant Francon and A5, towards Bettws Y Coed, ive never encountered a military vehicle, such as a camouflaged truck or land Rover coming towards me.
They obviously use the road, as there would be little use of having a camp in the vacinity, but the camp is a quiet one, traffic wise.
You occasionally see army personell on the Epynt ranges, especially when their Red flag is flying to indicate life firing in progress, but the carpark opposite the Storey Arms, is regularly used by the troops, and if one regularly uses the A470, as i did when i lived in South Wales, seeing the army vehicles was a regular event.
Now that i live in North Wales, i cannot remember ever seeing a military vehicle of any type passing me on the road.