Groups cannot be expanded in Microsoft Entourage
You can address messages or meeting invitations to groups using Microsoft Entourage. These groups can be found in the Exchange Global Address List, or GAL, by using the "Check Names" feature of message composition windows.
However, you cannot expand the groups to see their their members. This means that you cannot verify that a specific person is a member of a group. You also cannot check the individual free/busy status of group members. (Unfortunately, Groups lack free/busy status in Microsoft Entourage, too, so there is no way to check the free/busy status of groups without adding individuals to the invitation list.)
You may wish to send messages or invitations to individuals rather than groups when you need these capabilities. However, because many groups in the RIT GAL are automatically generated, you should limit your use of individuals' addresses to those times when you specifically need to verify membership or check free/busy status.