Voles are not native to Australia and are not established there in the wild. The entire family Cricetidae, which includes voles, has no natural Australian representatives. Australia's small rodents instead belong to different families, primarily the Muridae family, which includes native rats and mice like the house mouse (introduced) and various endemic species.
Australia's geographic isolation for millions of years resulted in unique marsupial and endemic rodent fauna. The only rodents naturally present are those that either evolved there or arrived through natural dispersal before human settlement. Voles, which are found across the Northern Hemisphere—particularly in North America, Europe, and Asia—never naturally colonized Australia.
It's theoretically possible that voles could be kept in captivity by zoos, research institutions, or private collectors, but they would not constitute a wild population. Australia has strict biosecurity and quarantine laws that make importing and establishing non-native species extremely difficult. Any such introduction would be highly regulated and monitored to prevent ecological escape.
If someone observes a small rodent in Australia and suspects it might be a vole, it is far more likely to be a native species, an introduced house mouse, or another established introduced rodent like the black rat or brown rat. Voles have distinctive features like shorter tails and stockier builds compared to many Australian native rodents, which could help with identification if needed.