As of WorkflowGen 5.5.1, you can disable the user/group deletion rule check for lists to improve the performance of user and group lists and speed up their display.
Note that the deletion rule will still be applied when you actually try to delete a user or a group.
To disable the deletion rule check, open the WorkflowGen web.config file (located in the DRIVE:\Inetpub\wwwroot\wfgen folder) and set the AdministrationEnableDeletionRulesCheck parameter to N.