Admin – Load existing admin template as a submenu page

You can add an interal link quite easily, it’s the same approach you use for adding custom items, you simply exclude a callback function and set the menu slug to the applicable URL, here’s an example.

add_action( 'admin_menu', 'add_user_type_link' );
function add_user_type_link() {
    add_submenu_page( 'users.php', 'Customers', 'Customers', 'edit_users', 'users.php?role=customers' );
}

Adjust the code as appropriate(required cap, naming, etc..).