I have the following configuration:
Beachheadcommunications.com is my admin site for WPMU. One of my sub-sites is MeshMarketer.com.
I have set up my Ultimate Facebook for both sites as sub-sites. In other words, there is an option to establish a plugin for Ultimate Facebook at the admin site and the sub-sites for Beachheadcommunications.com.
My UF widgets show for all of my subsites correctly, but they do not show for Beachheadcommunications.com no matter if I try to set it up for the admin site or the sub-site for Beachheadcommunications.com.
For Beachheadcommunications.com I have set it up for the sub-site the way I set it up for MeshMarketer.com before trying the admin setup for UF.