Configuration History:
Started with Split Domain, this is a fair amount of work.
Migrated everyone over to Zimbra.
GAL was pulled from both Active Directory and Zimbra.

Problem:
I think this will be fixed it Version 4.5, but as of 4.0.5...
Outlook Connector and Shared Calendars...
When adding a calendar to Outlook the GAL has their email address not their Logon account.

Example:
List has First_Last@example.com shows up in the list but their real logon account is. First_EmployeeNumber@example.com.

Solution:
In the admin screen of zimbra switch to Zimbra GAL only (note: we are not in the Authentication screen)
Then add the shared Calendars, it will work.

I have not tested what happens when I switch back to Both. I'm keeping it on Zimbra.