I found it necessary to copy data off the DVD and reformat the disc with the later version of UDF to avoid those problems.
As I recall, I was always formatting UDF, just to recover from errors. UDF was definitely not a reliable way to make backups. Now, I use DVDDAO to write my DVD backups (with auto verify), and I am having much better results. Of course doing that effectively formats the disk every time. DVDDAO also writes to CDs.
I too have a 1 TB USB drive, which works well with RSYNC (nightly). The main problem with that is that it is really slow, if I need to do a major restore (never, yet). Yes, it is running at USB 2.0 speeds, with the speedup patch applied. 1 TB is just a LOT of data.

To write the backups to DVD, I create some backup files (weekly, using BackAgain/2000, which does have some problems) onto my hard disk, then I burn them to DVD using DVDDAO. That also means that I have the original backup files on the hard disk (also copied to the USB drive), so I use them, when possible (almost always, so far). Of course, the BA/2K backups are limited to the "important" stuff, and I depend on the USB drive for the rest.
My third line of defense is a bootAble DVD (monthly), with another BA/2K backup of the "REALLY important" stuff, which I keep offsite.
http://hrbaan.home.xs4all.nl/bootAble/Note that this is a new address for bootAble (it is almost the same as the old address). I recommend the WPI installer version of bootAble, because that includes the ConfigMaker program, which makes it much easier to get started.