Ok, I figured some of this crap out. At least to the level that there doesn't appear to be anything wrong with either /dev/st0 or /dev/nst0. I can tar to either and read the information correctly. Maybe the problem is with flexbackup? I tried running a dump to /dev/nst0 with the command that flexbackup reports:
(dump -0 -b 10 -a -f - /boot | gzip -4) | buffer -m 3m -s 10k -u 100 -t -p 75 -B -o /dev/nst0
and everything works fine.
Any thoughts?
Joshua