Hi trumpyeah,
As long as the caps are authentic, you should be fine getting them into NZ.
NZ Customs has accepted the trade mark of New Era Caps, and therefore is responsible for making sure no fakes come into the country.
I found this info here: Link hidden: Login to view
If you want to ensure that your supplier is selling you authentic items, feel free to post a link and someone can take a look for you :)