The internal DVD-ROM drive on the TiBook is a Matshita DVD-ROM SR-8187.
What I was hoping to do was create a backup set on my (external, stationary) firewire Pioneer 103 DVDRW drive with a DVDR disk. (I figured asking the DVD-ROM drive to read RW might be a bit of a stretch.)
Then, when on the road, I want to be able to use that disk to restore any files that get broken from the Tibook DVD-ROM drive (built-in) that can run off battery and is thus mobile, which the DVDR is not.
Retrospect doesn't appear to see the DVD-ROM drive at all, certainly not as a legitimate device for restore or DVD source for a (read-only) restore session.