There is a site-specific patch (SSP) that seems to address problems with 'omnimigrate', SSPNT800_004
"omnimigrate.pl script is changed in order to properly export existing Data Protector IDB. "
I am not sure if this script would be valid for 8.1, I don't see why not. However, there are all kinds of other problems associated with 8.1, and for that reason, irf possible, I recommend that if you are going to upgrade, you only go to 8.0 or even 7.03
If you decide to go to 8.0, there are a few more SSPs that fix problems that were discovered after the release
You can open a case with the response center, either by phone, or through the SSO web site (preferable)
http://support.openview.hp.com/casemanager/incident-index
Click on 'Submit a Service Request'. Once you have a case open, request that a FTP site be created and that a copy of SSPNT800_004 be sent to the site. This will include a 'test' file with installation instructions, and how to run the script