I've since discovered that the password is simply Base64 encoded in the $OMNICONF/config/server/ID/idb.config file.
But today I discovered an undocumented omnidbutil feature:
omnidbutil -run_script sqlcommands.sql -detailJust create commands that you want to run in a text file. If you are on Windows, make sure the SQL file is saved in ASCII format rather than Unicode.
Much easier and I'm going to put that into the next edition of my Data Protector book.
Greg Baker is an independent consultant working on HP DataProtector, LiveVault and many other technologies. See more at IFOST's DataProtector pages at http://www.ifost.org.au/dataprotector.