Ted,

I had the exact same problem with my 7337 libraries being deleted between AIX
reboots.  I fixed it by putting the following lines in
/usr/lpp/adsmserv/bin/rc.adsmserv:

mkdev -c library -t 'ADSM-SCSI-LB' -s 'scsi' -p 'scsi2' -w '6,0'
mkdev -c library -t 'ADSM-SCSI-LB' -s 'scsi' -p 'scsi2' -w '3,0'

rc.adsmserv is the startup file for ADSM.  I put the lines at the beginning of
the file before ADSM is brought up.
You can get the exact commands and their parameters by using SMIT to redefine
your library as you have been
doing and looking at the smit.script file.