heya Ryan,
Im training to be Cabin Crew for them now, and go to the interview dressed and tidy corporate gear - i would still wear a tie at that stage. Once accepted and on training you dont have to wear a tie, but it is still very smart clothes, ie shirt and pants...
They assess your ability to withhold the grooming regs on recruitment day - so you need to presented in a way that shows that!
Good luck with your application - it really IS a great place to work