If Ledger isn't nominated for Best Actor, no supporting bullshit, and the film itself for Best Picture then I strongly suggest to every studio that they not bother putting any even vaguely Sci-Fi or Fantasy related film up for nomination ever again.
"Best Actor" and "Best Supporting Actor" are categories strictly designated by billing. Ledger did not have top billing, so it is impossible for him to be nominated for Best Actor.
IIRC, the posters we had in the UK had Bale and Ledger's names above the title and featured the Joker just as prominently as Batman.