I'm not the person you asked but I believe in the Foriegn Language film category the country has to submit the film for it to be considered. They instituted that rule during the Cold War to avoid socio-political flaps like the Boris Pasternak Nobel prize thing. Since The Passion is an American production I don't believe it will be submitted for Foriegn Language Film Oscar.
A foreign language film is defined, for Academy Award purposes, as a feature-length motion picture produced outside the United States of America with a predominantly non-English dialogue track.
I thought this might be something that the Academy would have to deal with. I guess not.
You are correct. Gibson's film cannot be submitted as a foreign film.