In Outlook 2003, if I go File -> Open -> Other User's Mailbox and type in the name of the hidden user I receive the error "Please select user accounts only.".
If I unhide the user from the GAL, update the GAL in Outlook and repeat the above steps it works fine. I then have to rehide the user.
Should it be possible to add a shared mailbox of a user hidden from the GAL without first unhiding them? Is this a bug?