The person I work under has vehicles under personal insurance.
As for the Sprinter, I'm not sure how the insurance is set up for that, since that's under another person who is an independent contractor (it's so convoluted).
It's convoluted on purpose because everyone is trying to finesse the insurance company and not have to pay additional premiums.
Push the issue they should file it under their primary insurance for whoever the vehicle is insured under and then it will slowly work itself out.
If they make a big deal tell them to pay out of pocket, this is the cost of doing business and by having proper insurance is that cost. Unless you signed paperwork saying you will assume all liability