I think his theory is that since all baptized JWs are "ordained ministers" and volunteers who go door to door to preach thus having direct contact with a child (or at least the possiblity of such contact) then everyone who goes in service should apply.
That differs from other religious organizations whose members are not considered "ordained ministers" (WTS own description of baptized JWS) and who do not engage in preaching from door to door.
The most recent instructions I saw was that the WTS wants their elders to comply. It's obvious from the link above that the law clearly applies to them and I could see where it would apply to MS as well since they could be placed in a position of oversight of a child (cleaning the hall, FS groups, etc). I know here in the US, the WTS has argued sucessfully that clergy privilege laws apply to JW elders so I don't see how legally you could say they aren't ministers.
I think having all comply is probably a stretch. They'll likely argue that the rank and file go out strictly on their own accord and have no direct appointment from the WTS.
I can't believe the Legal department hasn't already gotten the WTS to lay off the "ordained ministers" title applying to all JWs. I'll bet if Unthank wins, they'll drop it.