My experience so far - I'm in Victoria is that there can still be a Gap while an inpatient in a Private Hospital - for me this has been for Pharmacy and Pathology though I had reached a limit on my pathology that meant my gap was capped. with my pathology - the health fund and medicare co-contributed and I paid a Gap.
My understanding though was that inpatient Gap expenses did not contribute to the Medicare Safety Net while Outpatient gaps did. Once you reach the safety net - I think you are guaranteed to get 80% of the out of pockets back but only for out of hospital expenses.
http://www.medicareaustralia.gov.au/public/services/msn/index.jsp
I have not had any of my imaging tests as an inpatient so I am not sure about that. It does help though to use the one provider because within a certain timeframe (not sure what) it may be classed as the same "episode" and the costs start to reduce.
I have a literal box with about 8 separate folders to manage the billing and paying - awaiting medicare cheques, MBF cheques, paying Gaps etc... I am still waiting on a Medicare cheque for my pathology from my surgery.
My tip - Copy all of your invoices. If you submit to Medicare and do a dual claim they take the invoice and you have no record of your charges and out of pockets - also they get lost!
Amanda xx