The entire unmarked clip of the 1995 Oscars can be found here. David Letterman introduces the best picture category and then introduces Keanu Reeves who takes the stage and presents Pulp Fiction. It starts at the 12:11 mark and Keanu appears around 12:29. At the 40:50 mark you can see a flash of Keanu in the audience. Many thanks to Alexandra for sharing the video.
If you watch as they span the audience in the clip below, you can see a flash of Keanu in the audience.