// get the node id for the group
// expecting site urls to be in format group/group-name
  // HACK: get the internal (source) url from the first part of the path with arg, expecting to find 'group/group-name'
  $group_url = drupal_lookup_path('source', 'group/'.$args[0]);
  // extract the group node id
  $group_url_exploded = explode('/', $group_url);
  $args[0] = $group_url_exploded[1];

return $args;

http://www.ninelanterns.com.au

Add this arg code plus set first argument as "OG: Group nid(s)"

Views argument handling code: get gid from pretty group path

drupal

PHP