You definitely can, I have paid for tickets in AUD in the past.

However, I came unstuck when I wanted to cancel a ticket and online it would give me the option of doing so without penalty, but it failed because online the system could only process a refund in USD.

When I rung and queried I was basically told bad luck. Which in reality wasn't a major problem because going by the fare rules I should have been slugged a change/cancellation fee anyway I was just trying to get out of it because it would have let me online if I had paid in USD.

In any case my point was that if you think there is a chance of making changes or cancelling your reservation, it's probably going to be simpler down the track if the ticket was issued in USD.