If you can't pass the normal beep type testing, there are various hoops to jump through, but one possible process is that you can be approved to do an operational hearing test with an ATO where you get in the aircraft and prove you can operate in the air effectively.
CASA might not give the option to an individual based on their assessment of the circumstances and actual medical condition, but it's a possibility anyhow. I know they do this for degraded hearing, but not sure how applicable it is to full loss in one ear. Good luck anyhow.