Once you tell iCloud to connect to Outlook, iCloud begins creating a new primary folder in Outlook called "iCloud" and a number of subfolders called Contacts, Reminders as well as Home and Work calendars. It then proceeds to move data, without asking, from your main Outlook folder.
According to Bob Lewis at InfoWorld, the only way to reverse the operation is to uninstall iCloud and then restore your PST file from a backup. You do regularly back that up, right?
The problem with this in a corporate environment is there are no PST files, at least not for live data. Outlook keeps all of your key information in an OST file that is locked to your Exchange user account. When that data is trashed, the only way to restore it is through the backups in place by the IT department. Trust me, Exchange admins don't like being called during lunch to restore a user's mailbox because an unauthorized third-party tool deleted all of their contacts.
Office Watch has a few articles on how Outlook and iCloud interoperate. Both the iCloud and Microsoft Outlook and Problems with iCloud and Outlook articles recommend you avoid using these two pieces of software together.
There will always be a struggle between users that want to bring in outside tools they are comfortable with and IT departments that would have an easier time if PC's were locked down to just a few approved apps. Apple's iCloud is another example of why users should work with the IT department and not behind its back. Not only would they find out iCloud is a bad idea, they would learn they don't need it. Exchange is a far better cloud.
Even if you have a standalone version of Outlook, you should think twice before connecting it to iCloud.