Hazza,
The answers are
Yes and
Yes
It is not that simple, as the enforcement costs for the ATO to police all biodiesel makers would be horrendous and would cost the ATO more that they could ever recoup in tax.
I have yet to hear of a biodiesel home brewer being contacted by ATO or any other agency to ensure that they pay the excise. I do know of at least one home brewer who advises that he has registered with them and is paying the excise.

Regards,
Tony