Critics and Academy voters have never completely seen eye-to-eye when it comes to Oscar nominations, but critical praise for a film can surely influence a film's chances for Oscar recognition. I don't know if someone has actually done this, but surveying the ratings of all nominees for Best Picture in the last ten Oscar ceremonies (since the 68th) in Rotten Tomatoes yields very interesting results. For one, none of these 50 nominees got a Rotten score (59% and below). The closest to a Rotten score was the 61% of Chocolat (2000). Interestingly, the fifth lowest unadjusted (the number of reviewers differs per film, with generally more critics reviewing more recent films) is Gladiator, the Best Picture winner in 2000, with 77%. In fact, only four of the 10 winners got ratings of 90% and higher, with The Lord of the Rings: The Return of the King (2003) being the highest at 95%, followed by 1998's Shakespeare In Love (94%) and last year's winner, Million Dollar Baby (91%). Out of all the 10 winners, only The Lord of the Rings: The Return of the King was the highest rated among the films nominated in its year. The big champion (unadjusted) is the 1995 nominee Sense and Sensibility, the only film to get a rating of 100%.
Of course, we have to take into consideration the fact that, as mentioned above, the earlier movies generally have less reviewers. If we use the complicated weighted formula used by Rotten Tomatoes, the same three Best Picture winners have the highest weighted scores, and Gladiator is still the lowest. But this time, the big champ is The Lord of the Rings: The Two Towers (2002), with a whopping grade of 98% from 201 reviewers.
But the nominees aren't always what the Rotten Tomatoes critics think are the best. There are many films with higher ratings that failed to get a Best Picture nomination, so a very high score here doesn't necessarily mean a nom. Still, it's probably safe to say that if a film's score is Rotten, then it won't be nominated for Best Picture. That would mean that Oscar-buzzed Jarhead (Rotten at 58%) will be ignored for the top prize, while Good Night, and Good Luck. (94%, 151 reviewers) has a very good chance for one of the five slots.