that may not be quite right squad. it may be ok on a voluntary basis and provided the diabetes is well controlled. i don't believe you can drive a public service vehicle (a bus for instance) though, even though things have changed in recent years and people are beginning to realise that well controlled diabetes doesn't pose the huge threat to the public that it used to be thought.
i think a lot would depend on the organisation, and their insurance company, that you are doing the voluntary driving for,