Lisa Gerrard doesnt appear on the ost at all. She was originally commisioned to do it but Gibson decided not to go with it, althought she did record much or all of her own version.

From http://www.filmtracks.com/titles/passion_christ.html
"Debney received the job in October, 2003 after the previous composer had been dismissed; Debney was so thrilled by the prospect of being involved with the project that he wrote some sample material for Gibson that ended up being used in a trailer for the film"

Part of track 15 - Ressurection from the OST is essentially a re-scoring of the trailer music but i still much prefer the trailer version. Other tracks like Crucifixion keep alluding to the trailer music too which just annoys me when i think how good it should be.