Dish TV appear to have made the app available on Google Play
So I imagine you could load it on the Google device if it isn't on it already. It won't be on the US and Australian versions, so make sure you are buying the NZ Google TV thingee.
I have just bought the Dish TV device and so far I love it. I haven't used it for streaming Freeview although I have checked the stream out and it works fine.
The Dish TV device is using Android TV which is exactly what is used on the Google TV device.