Hudson,
There is no 737NG's on the NZ register so it is impossible to hold a 737NG rating on a NZ licence.
If you have it on an Australian licence you can get it put onto your NZ licence using the TTMRA forms, under the TTMRA the NZ CAA cannot prevent you from holding the rating if its on your Australian licence (note this still requires a 737NG to be placed on the NZ register).
S