Naturally, the last part of your question is the kicker, but according to "the fine print", you'll be OK.
"Arrivals: Platinum and Platinum One Qantas Frequent Flyer members may access Qantas Domestic Business or Qantas Club lounges upon arrival, if you have travelled that day on any flight with a Qantas (QF), Jetstar (JQ, 3K or GK), Emirates (EK), China Eastern (MU) or a oneworld member airline marketed and operated flight number on your ticket."
