Backup Exec 2012 has all kind of strange issues. The main one I've found is that backups can work fine one day and get a writer error the next. The quick fix is to reboot the server but not all customers can appreciate that.
They really need to fix this problem. It has been going on for many versions, but it appears worse than it used to be with Windows servers.
Backing up VMware is easier than ever, except when you do Debian versions. It doesn't appear to work no matter what way it is configured. I haven't yet tried it with the VM turn off. Hard to do on a production server.