Is search index updated on comment updates?

Is the implementation of hook_comment() necessary for this module to reindex a node after its comments have changed?

Something like this:

/*
 * Implementation of hook_comment().
 */
function instant_search_comment(&$a1, $op) {
  switch ($op) {
    case 'insert':
    case 'update':
    case 'delete':
      global $update_node_index;
      $update_node_index = is_array($a1) ? $a1['nid'] : $a1->nid;
      break;
  }
}