AFAIK, towing mirrors are compulsory if the cars mirrors don't give a full unimpeded view down the entire length of the van.
The easiest way to check this is to have someone stand at the rear corner of the van, if you can see that person clearly then you won't need extension mirrors, if you can't, you will.
No matter what type of rearview camera is fitted, you won't be able to see that person in that camera, nor see down the length of the van with a camera, so mirrors are required.
The above test is used by the Police if they pull you over for not having mirrors, so I have been told.