Oscar Hammerstein?
Hammerstein is right. How about this:
Who’s the only actor to win an Oscar portraying a character named Oscar?
Re: the OP, I don’t think any film where the actors consist of clip compilations should count. Just my $0.02.
I know! I know!
Walter Matthau as Oscar Madison in The Odd Couple.
Weren’t there are lot of loosely stitched together star vehicles that were made to entertain the troops during WW2? Since each of the stars had their own turn on screen, you couldn’t really call the performances cameos. They had to have had a number of Oscar winners in them.
For JFK (made in 1991), there are five previous winners and one future winner.
What about Donald Sutherland?
According to the Internet Movie Database, Donald Sutherland has never even been nominated for an Academy Award.
Nope, Matthau won for The Fortune Cookie. Wasn’t even nominated for that film.
Was it Edmund O’Brien, Best Supporting Actor as Oscar Muldoon in “The Barefoot Contessa”?
Since this was originally posted, both Tim Robbins (competitive) and Harry Belafonte (Honorary) have won Oscars, putting the film’s total to 14 now.
Has’nt Donald Sutherland won something in the meantime?
Nope, still nothing.
Not even for playing the teacher in the alternate ending of Big?
Takes out Nic Cage leather jacket. “I am a baaaaaaad man.”
The answer to this question is “yes.” Well done! 
It wasn’t asked but I’ll volunteer anyway that Roseanne is a TV show that had at least 4 Oscar winners:
-Estelle Parsons (Bonnie & Clyde) was a regular as Roseanne’s mom
-Shelley Winters (Diary of Anne Frank & Patch of Blue) had a recurring role as Bev’s mom
-Red Buttons (Sayonara) had a recurring role for a few episodes as Bev’s boyfriend
-George Clooney (Syriana) was a first season regular (many years before his Oscar wins)
Can any TV show match that?
Just a mild bump since Oscar season is nigh.
It should be noted that The Grand Budapest Hotel has 15 Oscar nominees in its cast (including 4 winners). If Edward Norton wins for Birdman (he’s a likely nominee), that will raise the film’s total to 5.
Speaking of Birdman, Michael Keaton is likely to receive his first Oscar nomination for the film. If he manages to win, he will be the 14th person to both win an Academy Award and appear in a Batman film–a record for any film franchise.
The other winners
Batman: Kim Basinger, Jack Nicholson, Jack Palance
Batman Returns: Christopher Walken
Batman Forever: Tommy Lee Jones, Nicole Kidman
Batman & Robin: George Clooney
Batman Begins: Christian Bale, Michael Caine, Morgan Freeman
The Dark Knight: Heath Ledger
The Dark Knight Rises: Marion Cotillard, Anne Hathaway
And of course, Ben Affleck is cast as Batman in Batman v Superman: Dawn of Justice which will also include Jeremy Irons (Alfred) and Holly Hunter in its cast.
In an ensemble cast of 14, Murder on the Orient Express had five winners, one honorary winner (lifetime achievement), and four actors who were nominated without winning, plus a French actor who had won a Cesar. Many of the actors who were British had won BAFTAs, and several of the cast members had won Golden Globes and Tonys.
Here’s the list (probably badly formatted):
Albert Finney
… Hercule Poirot (nominated many times, but no wins)
Lauren Bacall
… Mrs. Hubbard (no wins; honorary award in 2010)
Martin Balsam
… Bianchi (yes, for A Thousand Clowns, 1966)
Ingrid Bergman
… Greta (yes, for Gaslight and* Anastasia*, both prior to MoOE)
Jacqueline Bisset
… Countess Andrenyi (no)
Jean-Pierre Cassel
… Pierre (as Jean Pierre Cassel) (no Oscars, but he was French, and did win a Cesar)
Sean Connery
… Col. Arbuthnot (yes, but not until 1988)
John Gielgud
… Beddoes (yes, in 1964, and 1981)
Wendy Hiller
… Princess Dragomiroff (yes, 1959)
Anthony Perkins
… McQueen (nominated, no wins)
Vanessa Redgrave
… Mary Debenham (yes, in 1978; had nominations prior to MoOE)
Rachel Roberts
… Hildegarde (nominated, no wins)
Richard Widmark
… Ratchett (nominated, no wins)
Michael York
… Count Andrenyi (no)
Director Sidney Lumet was a many-times nominee who was given an honorary award in 2005. The costuming, music, cinematography, was done by winners and nominees.
Usually when Hollywood tries a “star-studded” stunt like this, it flops, hugely, but this is an excellent film. Even Dame Agatha Christie, who was consistently disappointed in the film versions of her books, thought this film was perfect.
In fact, it’s not just money (although, it is money) that prevents these sort of multiple big name films from getting off the ground. It’s the fact that the common wisdom is that they will do poorly.
As a side note, Ned Betty occasionally played Dan’s dad, and has an Oscar nomination for his role in Network.
I count six in recurring roles for St. Elsewhere, but the only two who had what I’d call a genuine lead or recurring role were Denzel Washington and Helen Hunt.
::checks IMDB::
Hang on – Spielberg won the Best Picture Oscar by winning the Oscar for directing SCHINDLER’S LIST, but Liam Neeson got nothing for getting directed as Schindler?
That was the year that Tom Hanks became Serious Actor, the first of his back-to-back wins.
But Neeson was nominated, and as long as we’re discussing Batman-franchise nominees, we might as well add: Michelle Pfeiffer, Danny DeVito, Uma Thurman, Gary Oldman, Ken Watanabe, Tom Wilkinson, Maggie Gyllenhaal, Eric Roberts and Tom Conti (another 10 people), plus Burgess Meredith from the original Adam West movie. 25 total.
Liam Neeson won his Oscar for playing Oskar Schindler, which is close. He also appeared in a film with four other Oscar winners: News on played a small role in “The Bounty.” Laurence Olivier also had a small role with larger parts played by Anthony Hopkins, Mel Gibson and Daniel Day Lewis. Only Olivier had his awards when the film was made and Gibson did not win his Oscar for acting.