I have no idea why Air NZ will happily pay for you to go to a United Lounge in most other places Air NZ flies, but not SFO. It's very bizarre. I believe this is the same for Elite Partners, which is arguably worse.
They will give you a US$25 voucher when checking in at the airport. If you are departing at night, good luck! You may find most of the stores will be closed. However, they all seem to accept the voucher. The food options are pretty terrible if you are looking for anything remotely healthy.