Are you sure that everyone driving a vehicle with DOT numbers needs a Med Card? It's my understanding that the DOT registrations that are for intrastate only do not require med cards, safety audits, logs, etc. These would be the DOT numbers that have a state sufix at the end like NY, WI, etc. My friend has a 20,000 GVW rollback truck for his business, it has the DOT numbers that end in NY and he does not need to have any of the above. He can only use the truck for in-state (NY) business. I'm not sure if this is the same for all states that require the numbers for in_state business.
Now that you ask, No I am not sure.
I know what you mean with the USDOT # that ends with NY(for example) but i have never seen that in WI. I was under the impressison that if you need a DOT# you need the whole package(Med Card, safety equip., etc).