I think you should simple create a job or script for connecting through SSH using a public key and disable the Antivirus service from Isilon when the backup job start and run another one when the backup job finish in order to enable it again, I think is simple but a useful workaround.
I hope this solution can helps!
Perhaps applying timely policy exclusions on those server(s) that are running your nightly Tivoli "exe" backup software. Afterwards, reapply the standard server policy back on those servers (automation task or a server task can be setup for this)
TSM Backup/Archive client and McAfee VirusScan Enterprise
Also, may consider excluding the actual "Backup Folder" during those nightly backups.