When attempting to add another user's (shared) contacts to your own Outlook, you'll notice that you won't be able to access these contacts from the Outlook address book. Additionally, when right-clicking the shared contacts folder, you'll notice you can't choose to display the contacts in the Outlook address book.



The reason for this is that Outlook simply does not allow it. Quoted from an Exchange engineer:

Engineer from exchange server
By the current outlook design, it’s not possible to implement the shared contacts folder in the Outlook Address Book. The Outlook Address Book tab feature is ‘by design’ unavailable for shared contacts folders and this is hard-coded in the Outlook   ...