The SYD Business Lounge staff will need to see an accepatable BP or a Qantas WP (Platinum or higher) card. These are most usually not scanned. You don't need to show ID or a BP to pass through security before accessing the lounge.
Sorry, I did a really bad job of phrasing my question. I'm asking about at ADL--can I use the QC on arrival, or are they strict about requiring a departing flight?