We had the same problem with our environment. AIX Master, AIX Media server and Windows Media server. All running NBU 6.5.2A. We have installed about 5 binaries and this problem seems to have been resolved. I would contact Veritas support and get the latest binaries for 6.5.2A.
As a work around when starting NetBackup, we would start the master server first and run vmdareq over and over until all of the tape drives show available and not showing a scanning status. Once vmdareq displayed all tape drive available consistantly, we would start the media servers.
eebinstaller.1406132.1.rs6000
eebinstaller.1410910.2.rs6000
eebinstaller.1429781.1.rs6000
I believe these 3 are the last one we installed.
I hope this helps.
Mike Wigington