I wondered how would the company practically verify that they were wearing a helmet?
It seems quite a dangerous route to go down because you could have a claim and then the other party fills in the forms a few months later and have a section on helmets and it would be overwhelmingly tempting to say no they weren't wearing a helmet. Once you arm someone with the knowledge about helmets and perhaps even a section dedicated to finding out whether they were wearing a helmet people will be exploiting it.
I remember being interviewed by an insurance investigator and when they found out I was a cyclist you could almost imagine them jotting down on the piece of paper - cyclist, must be lying, company should dismiss anything they say.