Here's the word from someone else who will be there.

The Academy Awards will air live from 5:30 to 8:30 Pacific time. The Sacred Harp singers will perform approximately an hour into the show. They are billed as "Sacred Harp Singers of Liberty Church" because Liberty Church in Henager, Alabama is where the recording session for Cold Mountain took place. There will be @37 singers from Georgia, Alabama, Texas, New York, Rhode Island, Massachusetts, New Mexico, Illinois, Michigan, and Minnesota.

They will be singing two numbers on the show. The first is the Elvis Costello song "The Scarlet Tide" from Cold Mountain. Allison Krauss will be singing the song as she did on the soundtrack.

Right after that, the Sacred Harp singers will be singing Liberty, pg 137. (not on the soundtrack)