Hi Philip,
First of, I would query whether you are backing up too much. The Information Store automatically grabs everything Exchange related, so backing up Exchange Mailboxes actually means you are backing this up twice.
As to why Veritas offer this option in the first place, it's because prior to Exchange 2003's recovery storage groups, deleted item retention, etc etc, this was the only way you could restore an actually deleted email.
The Information Store is all you need to restore an Exchange database.
That said, you are likely to want to restore the server itself, so you should find backing up C: and System State additionally useful.
You seem to indicate you are happy to take our word for it that your backups are sucessful. That is the surest way to be wrong.
I would strongly advise performing some test disaster recoveries, and proving to yourself that you are backing up everything necessary.