I work with a lot of Aborigines and I don't really see it, nor am I aware of any aboriginal ancestry on his father's side (and I think his mother's American, though I might well be wrong).
However, it's quite possible. Many Australians who had a small amount of aboriginal ancestry either did not know it or did not mention it until recent years. This is the main reason why the number of people claiming aboriginal descent in the census appears to have "jumped" from less than 1% of the Aus population to over 2% in only 10 years!! Now it is considered quite prestigious in many circles to eek out that aboriginal ancestor even if you have no links to the community as such ... a nice change I think!
His dad was an Australian pro tennis player and played Davis Cup for Australia. Hence the ongoing "Australia rejects Dent"; "No, Dent rejects Australia"; "No, wait a minute, Dent rejects USA (after accepting their funding)" debate. Yawn.