I don't know the answer to your question, but I'd say your best bet is to get in touch with a mortgage broker, they will be able to give you guidance on this.
From what I gather, it's about what the bank can see on paper; I have friends who bought as a couple but the house is only in one of thier names using one of their kiwisaver - the other will then use their kiwisaver as a first time buyer to buy a second property. Technically there will be no record of previous borrowing in NZ I'd guess that you'd be fine to purchase as a first time buyer....