"says that CASA will not recognise/permit "Experimental" aircraft from other countries"
I don't know this is true, i have seen many experimental registered aircraft with OS registration come through the Gold Coast area on their way somewhere, lots of N numbered EXP Lancair's flying the South Pacific, all the Ericsson air cranes fighting fires are EXP
I imagine they could do an exemption if it was the case because lets face it, from entering Australian "Airspace" to land at Darwin doesn't really pose a real threat to anyone. ESPECIALLY if these experimentals had already proven themselves and covered 18,000 kms before they arrive.