In Oz you can examine in a simulator without a current medical. You can examine in light aircraft on a class two medical. But first you need a Part 61 licence, and to get that you will need at least a class two medical for CPL (Aussie Bob correct me on that if I have it wrong) and class one for ATPL issue. Once you have the licence it never expires even if the medical does.
While ICAO licence conversion to the Oz ticket is do-able by jumping through a few hoops, there seems to be NO recognition of foreign examiner qualifications.
As a general rule (with transport category aircraft at least) you can only examine items on which you have been assessed proficient within the applicable time limit e.g instrument rating current within last year to conduct IPC, proficiency check on type within previous two years to conduct Type Rating test etc.