Changing default file permissions for group?
I don't believe Drupal or Omega will be setting the default permissions to 754, more likely it's a default that your webhost has configured.  Things I would check would be:


If you upload a file as ftpuser, does it default to 754?  If so, then they have a default permission set to 754.  You could contact the host to see if they are able to change that.
If you manually create a file using PHP, does the file get created at 754? If so, same as above.
If they're created at something other than 754, then it's likely Omega or Drupal that is doing that, but again I don't believe that's the case.


In any event, I've successfully gotten around this problem for many users by integrating a web-based file manager like IMCE, which allows you to manage files without using FTP.