Had no probs on a 495 visa.We are on the 495 visas and changed our driving licences over when we arrived.
I think it is probably easier to change to a SA licence for a few of reasons.
1. Excellent form of ID for rentals/banks etc
2. Without an Aussie Licence you need to carry your UK Licence and passport whenever you drive, bulky whereas the Aussie licence fits in your wallet.
3. The Aussie cops generally don't know or care about the different visa types and expect you to change it over within the 3 months.