I suspect that without adequately trained pilots, FA-18 hornets would get shot out of the skies by the Russians pretty much immediately. Which would be quite an expensive waste. I don't know if the Ukrainians ever had anything similar in their airforce, but I'm pretty certain that they've never had FA-18 hornets or super-hornets.
Unless you are suggesting we also send over pilots? I doubt any Australian government would want to go that far in a conflict of this sort at this stage.
Bushmasters don't need anywhere near as much training to use as an FA-18.