I've always played all WE's as a single unit. So 1 die for dangerous terrain or 1 die for teleport etc.
If questioned I usually show this in response, highlighted relevant part as teleport states 1 d6 per unit.
Quote:
3.1.1 War Engine Formations
War engines are so large they usually operate as single units.
Although only one unit, the war engine is still a separate
formation, and all of the rules that apply to formations apply to
it also.
Some smaller war engines like Baneblades operate in
formations of more than one unit. War engines count as being
within formation coherency distance if they are within a
distance equal to their starting damage capacity x 5cm of
another unit from the formation. For example, a Bandeblade
has a starting damage capacity of 3, and so will be in formation
as long as it is within (3x5) = 15cm of another unit.