No you should be fine. Exchange Mailbox backups and restores work through Outlook rather than directly through the mailstore, so effectively Backup Exec will open Outlook to access the users mailbox, and restore the selected items through there.
One thing to note though, while I can't remember why or how it happened (straining to remember what I did several years ago), the last time I tried to restore some e-mails for one of my users, for some reason as well as restoring those e-mails which the user had deleted, it also restore the other e-mails, so they ended up with two copies of the mails they already had. I think in my situation it was a case where I didn't know exactly which mails had been deleted, so expected that if I restored all of them while telling the restore to skip items which were already there, it would be fine, however it didn't skip them. So unless you know exactly which items you need, I'd suggest creating a temporary mailbox, restoring the items there, and then you or your user can retrieve those items that they need.
Keith
