I have an award ticket from IAD-LAX on UA which includes 1 free checked bag. Later that day, on a separate ticket, I will then fly NZ from LAX to SYD via AKL.

Given UA and NZ are *alliance, Will/Can UA check my bag all the way through to SYD?

Is it at the discretion of the agent or a matter of course?

If yes, am I right in thinking because my bag is free on UA it will also be free on NZ.
Thanks