We were asked for an AOS. I am living with my husband in his country and we both supplied letters of employment to the SMO, but we were still asked for it. You have to wait for immigration to ask for a AOS and they email you the letter which has to be taken to centrelink as you can't do anything without that original letter. Once you receive it get the person/s who are going to do it to call centrelink and make an appointment (which in our case was 1wk later) and they tell your assurer on the spot if it has been approved or not and send it electronically to the embassy/DIAC that you applied to within 48hrs. We didn't need a bond, so not sure how it works if you need a bond.
It really comes down to the SMO's discretion as I know of other couples in the same boat who were never asked for it.
Hope that helps