https://www.news.com.au/national/politics/elite-cultural-ins…
Notably:
No proof of eligibility is required to claim the discount
Not to mention it would be horribly offensive for anyone to ask anyway.
I've had a look and so far seen these discounted tickets on offer from the Sydney Opera House and the Sydney Symphony Orchestra, and they're incredibly cheap (eg $13 for Birds of Tokyo concert with the SSO) but they are also, understandably and correspondingly, in less attractive locations and very very limited in number.
By way of examples:
https://www.sydneyoperahouse.com/mob-tix
https://www.sydneysymphony.com/concerts-tickets/whats-on/mob…
https://australianballet.com.au/your-visit/ticket-informatio…
https://www.brunswickmusicfestival.com.au/event-info/mob-tic…
https://www.mso.com.au/terms-and-conditions
Edited to add: in addition to eligibility not being checked (and really impossible to check), all of the sites include wording that this includes "First Nations people of other countries" which surely has to include everyone because everyone is an original inhabitant of some place.