Normally, If you are on a BES, there is no need to manually backup your phone, because, all important data is wireless backuped on the server.
However, if you choose to make backups anyway then the article is correct, still someone has to get his hands on the files.
BIS has no wireless backup. If you need to backup your device settings, you should store them at a safe location.
But, if someone is able to remotely get access to your PC in the office, where you most likely store your backups, he has access to your mail, your files, anything, no need to hack the backup files of the BB.