Adding user privileges to Schematic Dataset creates errant "ERROR 999999" Error executing function. Failed to execute (ChangePrivileges)., but the actual function of changing rights is functioning properly.
To get away from Error 999999, install the ArcGIS Desktop 10.1 SP0 client and you will be able to view and alter rights successfully on an ArcSDE 10.0 SP4 and SP5 geodatabase.