It is up to UA and not NZ. Upon arrival in the US, all pax must claim baggage and clear customs. This is true for all airports and all airlines. After clearing customs, there is an airline baggage recheck area where you drop your bags if they have been through-checked. So if UA has checked your bags through to RAR then you can drop the bags here. If UA did not check your bags through to RAR (and this is strictly a UA issue), then you must take the bags with you and use the NZ check-in counter in T2. Unfortunately it probably isn't open at the time that you arrive on UA -- thus the comments from NZ. And there is no place to store luggage at LAX. So try very hard to have UA check your bags through to RAR when you start your trip. If you cannot do this, then your best bet might be to rent a car at LAX (this is often available for under USD 20 per day).