First up, understand that the premier loyalty hook for the AAdvantage program frequent fliers is UPGRADES. And as such, there are many varied and intricate ways to get upgrades on AA...
For those who credit to QFF, the most useful way is to purchase an "instant upgrade" ticket when making a booking with AA. ("Generally", this gives you a confirmed seat in a premium cabin, at the time of booking, but often with less flexible conditions than a full price premium ticket.)
However, for those who use AAdvantage, there are a
multitude of ways to upgrade; from the
moment you make your booking right through to
just before you board the aircraft.
The
final upgrade opportunity (for AAdvantage members) is
the gate upgrade. You may notice "upgrade lists" displayed on monitors near the gates, at many locations where AA departs from. This is the
gate upgrade list, and to see your name on it, you
generally need to request the agent at the gate desk to put it there (
most often due to one's AAdvantage status.)
This magnificent list is actually a ranking order, determining who will get an upgrade to any empty premium cabin seats left on that flight. (
Unlike Qantas, AA doesn't like to fly with empty premium cabin seats, they prefer to fill them with loyal customers via this final upgrade methodology.)
This particular upgrade list is noted on the manifest that the Flight Attendants receive. And it allows them to fill any remaining empty seats, in the premium cabin, once boarding is complete (e.g. say a Full Fare customer "no shows" leaving an empty seat).
Oneworld status is
not a route for getting your name on this list.
(Although, 1W members may get on this list via other routes, e.g. a First Class customer taking an involuntary downgrade, due to reroute, will most likely be the first name on the list, regardless of whether their affiliation is with AAdvantage or another 1W member airline.)
Now, as for the FA on the flight, for simplicity's sake many of them simply see a Oneworld status member as the equivalent in AAdvantage, so where it states "Emerald" they read "Executive Platinum", and apply the same benefits (even when the home airline benefits are
not a privilege given to 1W status holders, e.g. like getting on this upgrade list). [
There is an advantage to this vision, however, as some FAs may give you freebies from the BOB menu, if you are in Coach or on Eagle.

]