Seems extremely unlikely air traffic control wouldn't know of it, since it's potentially a >200-casualty mistake if it hits a commercial airline.

The rocket lab launch was south from New Zealand - and there aren't many planes flying around down there as far as I know.

I'm guessing only the final stage would still be airborne/in space once it orbited around to populated areas. And the second/final stage should be deliberately de-orbited for exactly this reason, right?