This SQL query will show you all the users that you have given special roles in Service Catalog:
USE mdb
SELECT [domain]
,[role_id]
,[user_id]
,[last_name]
,[first_name]
FROM [dbo].[usm_contact_domain_role]
JOIN [dbo].[ca_contact] ON [ca_contact].[userid] = [usm_contact_domain_role].[user_id]