Turning once again to the Commonwealth Electoral Act 1918, we find s184AA (emphasis added):
184AA Application forms for postal votes
(1) An application form for a postal vote may be physically attached to, or form part of, other written material issued by any person or organisation.
(2) For the purposes of the Copyright Act 1968, if a person other than the owner of the copyright in the application form for a postal vote reproduces the application form, the person is not taken to have infringed the copyright in the application form.
So, yes, it is entirely legal for a political party to send you an application for a postal vote (PVA) as part of their promotional material and then nominate themselves as the return address.
Provided that the party then forwards the PVA to the Australian Electoral Commission (AEC) by the deadline, it is all valid.
Yes, this does mean that the political parties probably track who applies for a postal vote through their kindly provided forms and, yes, it’s probably used to estimate how the postal votes will break in terms of preferences.
You can still use this to mess with the parties. If you’re planning to vote for party X, by all means lodge your PVA via party Y. For added amusement, if you’re planning to favour major party X whilst giving your first preference to minor party A, then lodge your PVA via major party Y.
Alternatively, lodge it directly with the AEC yourself if you don’t want any party tracking that you’ve done so.
That said, I do recommend not using postal votes unless necessary. I know that the trend over the last few decades has been towards more postal votes (because convenient), but it only makes counting the votes harder and introduces a risk that your vote won’t be counted at all.
Postal votes are an example of declaration vote: you have to seal them into an envelope with a witness declaration in lieu of the ballot box. This introduces the preliminary scrutiny described here.
The AEC has to check the completion of the declaration, the witnessing, and the entitlement to vote before the envelope can be opened and the votes admitted to a ballot box. It takes a lot longer, is observed by many scrutineers, and adds a lot of work to already stressed electoral officers.
Finally, don’t forget that the rolls close on 23 May 2016, so enrol now.
 And if you believe that I have a bridge to sell you. Also, AFAIK, all parties do this. Don’t criticise one for doing so unless you criticise all.
 Absent, provisional, and some pre-polls are other types of declaration votes.
 There are many reasons why people can’t vote in person, and that’s what postal votes are for. Please don’t do it just because it’s convenient.