You don't think DVDRAM will be fine for the amount he's backing up? I mean, the primary advantage that tape has as a backup medium is its size. The amount of data he has to backup is relatively small (my father's office just installed some monster-sized tape backups which they need primarily for all the space that's used by the desktop publishing division).

The advantage to DVDRAM, in my mind, would be far faster recording speed (faster than all other writable DVDs, I believe). You'd also have much faster seek times if you needed to replace data.