As a matter of fact, I sent my nomination list (which was mostly animation related titles) a few months ago. While I admit I did put some more notable Disney shorts on there (including the PSA short "The New Spirit" and the Safety award winning "Motor Mania"), I didn't leave out the other studios. Off the top of my head, I nominated Fleischer's "Superman", Lantz' "Barber of Seville" and the MGM shorts, "Red Hot Riding Hood", "King Sized Canary", "Mouse Trouble" (I had to choose between that and "Cat's Concerto"), and I think "Peace on Earth".
Regrettably, the only Warners short I put there was "A Wild Hare". However, after reading Michael Lyons' anniversary article on "Animation Scoop", I should've included "The Great Piggy Bank Robbery" as well. I'll try next year.