Hi Matthew,
There is a Quick Base API call that does pull up user data from an application. It is API_UserRoles. If you run it against an application it will give you the User ID, name, role, and user data for those users who are invited into the application. This will bring you back a lot of the information that is stored within the user table itself. There is a link to the entry for API_UserRoles include below and I hope this information is helpful.
https://help.quickbase.com/api-guide/userroles.html