I think Rick meant to say if you don't currently hold a FAA certificate you can do a paper shuffle and get a private certificate without a checkride. You can take either the instrument foreign pilot written or the regular US pilot instrument written and get an instrument rating added without a checkride. And the FAA will put your Dash 8 rating on it.
There's really not much reason to do that unless you fall into one category. If you can show the person who trained you for the Oz Dash 8 rating held a FAA CFI, then when you get a regular FAA ATP, the Dash 8 rating will jump over to it. Otherwise, you may as well just do a regular FAA ATP when you reach 1500 hours.
As Rick says, the requirements for the ATP will change 1 August 14 so be sure you pass your written before then. You will have 24 months from when you pass the written to complete the checkride. Starting in August you will have to complete a ground school with three classroom days and a couple sim sessions just to sit the written.