It seems there is a bug with Office 365 and we're not sure if its an issue with the client or the server but it is there. Apparently the only way Mac clients can get updates is to blow away the cache on their machines every time. We have tested this on a completely vanilla install of 10.8.1 with Office Updated to 14.2.3 we then add the client and verify the address is pulled from EWS. (takes about 5 minutes)
After the Address book was populated we added a test resource mailbox. After 2 days of send/receive, reboots and force quits we still didn't see the new contact.
Once we blow away the cache within ~\Library\cache\Outlook\{Number}\ it appears within 10 minutes. This is not only affecting us, there is a thread of users with the same complaints.