Do all these right-wing identities have a similarly slack attitude to legal compliance for their business interests?

It's hardly difficult to find out the law, you don't need a QC, just go to Google, type in "Local Government Act", pull the page up and search for "election":

Extraordinary vacancy in local authority or community board

(1) If a vacancy occurs in the office of a member of a local authority or in the office of an elected member of a community board more than 12 months before the next triennial general election, the vacancy must be filled by an election under this Act.

And on Kiwiblog and Whaleoil. That’s quite a lot of readers

Less than 10,000, if you exclude bots?

Not an electorally significant population - it's more that journalists give these sites more credence than they deserve.