What another worker does doesn’t mean it’s right, and won’t save you if you end up having a chat with VOSA/DVSA…
For me, if it’s got a tacho, my card goes in! After all, why has it got a tacho if it doesn’t need one? 
Plus you are working!!!
Van’s don’t normally have a tacho, so in this situation don’t worry about it. Yes it’s a bit confusing and a bit silly, but driving a van or a car for work is out of scope with regards to driving hours!