HomePod

There isn't an "Australian" version as such, other than the plug for the power point in the HomePod (and the HomePod Mini's power adapter) built for our type of power points. Happily the Kiwis use the same type of power points and have the same voltage so the HomePod would work in Auckland just as well as mine in Melbourne.

Last time I checked Apple had not yet made the HomePod or HomePod Mini available in NZ and I would imagine one or two have been sent over there by friends here in the "Big Island".

You'd have to have it in NZ to be definitive, but comments on other forums indicate that those posting had no problems with Siri on HomePod (& mini) in territories where the device is not yet sold by Apple or authorised non-Apple vendors.

I can understand how an Apple TV would not work in your example (though Apple TV is sold in NZ). This would be because it asks you to set the device for a country or region, for content delivery if nothing else, but this is different to being supported. As I understand it "supported" means that Apple has not officially released a product in a territory and will not accept it for repairs etc. This NZ authorised reseller in Auckland is a good example. They acknowledge that customers in NZ have the device, but tactfully remind that "Unfortunately iStore is unable to service HomePod because it is not sold in New Zealand."

While HomePod signs into your Apple ID account and appears in your list of devices it has no other region setting but as I observed, comments elsewhere indicate that this causes no problems.