I can confirm that this feature is NOT available with an australian iTunes account at the present time
Using Mountain Lion 10.8.3 and iTunes 11.0.2 (current versions on April 6, 2013) and one of the newer cards just released in Australia* I logged into an Australian account, clicked redeem and there was no camera button available.
Signing out, then in again with an american account revealed the 'use camera' button
As expected, scanning one of the new Australian cards* with the hologram on the front while logged in to the US store results in "This code must be redeemed in the Australian Storefront"
I hope we will get the feature soon - the camera recognises the number upside down, at 45°, with card tilted away from the screen and at 45°.
Very cool - hurry up Apple
*Older versions of iTunes or App Store cards will never work - when facetime redemption is enabled for our region it will only work new cards.
The new iTunes cards have a hologram on the front and the scratch panel has been replaced with a peelable sticker. The number beneath the sticker is surrounded by a black box to assist the camera in locating it.