Users Anywhere really means users... from anywhere! You can even get users from another Joomla site / database.
In the "Advanced" section of the Users Anywhere system plugin settings you can set up as many external Databases as you want.
To add an external Database, you need to give it an identifying "name" for Users Anywhere, and then enter the various database information: type, host, username, password, db name and table prefix.
You can also enter the "Domain" the database is pulling the users from. This is helpful to make URLs and image tags point to the correct domain.
You can then tell the {users} tag to pull users from the external database / site, by using the attribute database="...", where the value is the name that you set in the Database settings explained above.
{users usergroup="Customer" database="My External Database"}...{/users}
This extends the possibilities even further, allowing you to even handle multi-site installations and output users' data from multiple sites!