'Austraila' doesn't grant visas to those with serious criminal convictions.
I've no idea whether this is serious enough to count. If he gets jailed it might be, otherwise probably not.
The way to find out will be to apply online for an ETA (electronic visa). If it's granted to Australians either don't know or don't care about the conviction.
the visa form just says you have to declare any conviction of any crime or offence in any country, including one since expunged from the records. Then the officer reviewing your application will decide. So do as dzug advises.