I believe even all our 3.x documentation (well...not so sure about 3.1, but definitely 3.2 and 3.4) is still Public on SymWISE (but may not be too easy to find).
That's a NetBackup for UNIX 3.2 README (despite the very non-descriptive document title!)
Here's our End of Life statement for 3.1.1/3.1.5:
Feel free to PM me if you are looking for something specific - if it's still Public, I'm happy to throw you a link.
Thanks again! This may be wrong forum to ask this, but would anyone be able to please point me to technical documentation or white papers published before 3/6/2003 for Hitachi ShadowImage?