Just using PDT for rhetorical discussion, I wonder if an E-3 holder would be able to flow to AA mainline. The whole flow thing is much discussed and only time will tell.
I can see if an Australian were to weave the Magic Aussie Spell on some of the local talent and marry into a green card, it wouldn't be an issue. Not sure how the E-3 would affect the theoretical flow situation.
And the AA careers website doesn't address the 4-year degree issue at all (unless I've overlooked something).