NetBackup database support is documented in the Compatibility Guide: http://www.symantec.com/docs/TECH126904
The DB2 for NBU Guide describes the HOWTO from NBU point of view: http://www.symantec.com/docs/DOC5166
This is the sum-total of what we (as user Community) know.
How Lotus Mail Archive should be protected is a discussion you need to have with the Admins, or maybe look for it in IBM product documentation.
Your other alternative is to get hold of your local Symantec SE to put you in contact with the Symantec Regional Product Manager. This Product Manager will know who the relevant product expert is and channel your questions to this person.