Upvote:1
Yes it will, because your flight (although a code share) is flown by one carrier Etihad - I am also willing to bet it has a 4 digit flight number.
Once you arrive in Abu Dhabi you will spend time at the transit lounge and board your next flight.
At check-in, you will definitely be given two boarding passes Johannesburg - Abu Dhabi, Abu Dhabi - Sydney; and also possibly the Sydney - Auckland boarding pass.
In either case, your bags will be checked through to New Zealand.
The reason you may not be given a pass for the final leg at Johannesburg is because sometimes the flight reservation systems don't have the aircraft data to issue seats. In this case you'll pick up your boarding pass at the transfer desk in Sydney.
This is rare, but does happen.
However in all circumstances you will clear customs and immigration in Auckland and pick up your luggage there.
Upvote:2
If you can purchase all three flights as one ticket, your luggage will definitely be checked all the way to Auckland, and you will most probably get all your boarding passes at JNB. If you don't, you can pick them up at transfer desks along the way in Abu Dhabi or Sydney; you will definitely not need to go through Immigration or Customs at any point along the way.
But as Gagravarr says, if this is urgent and you want a definitive answer, call the airline instead of trusting random people on the Intertubes!