Your code (or other plugin code) can use the following Role Scoper function to output the users list for any group_id you specify:

$users = ScoperAdminLib::get_group_members( $group_id );

// call your e-mail send function (or by build your send list) inside this loop
foreach ($users as $user )
  echo ( " $user->display_name : $user->user_email " );

I'm not prepared to give Role Scoper the responsibility of sending e-mails.