Your question falls under the category of Security Administration or Platform Administration and is outside the scope of this discussion forum for SAS Macro, Data Step and SAS Language elements. The Security Administration piece of the Platform Administration documentation is a 239 page document. http://support.sas.com/documentation/configuration/bisecag.pdf
besides there being one mistake in your code ("Create xml query_logins.xml:" - should be changed to query_persons.xml), it worked just fine. It did exactly what I had asked, it brought me back an XML file with the usernames of all the people that have been manually added in the SAS management console.
With this info, I think I'll be able to write the code to do my own version of identity management. Thanks so much!