When a severe error occurs on the site, i'd like to be notified.
The easiest way is to add logging to the general log file in my opinion.
Is it possible to add the following rule to the feeds_log function?

watchdog('feeds', $message, $variables, $severity);

See code below for implementation

function feeds_log($importer_id, $feed_nid, $type, $message, $variables = array(), $severity = WATCHDOG_NOTICE) {
  if ($severity < WATCHDOG_NOTICE) {
    $error = &drupal_static('feeds_log_error', FALSE);
    $error = TRUE;
    watchdog('feeds', $message, $variables, $severity);
      'id' => $importer_id,
      'feed_nid' => $feed_nid,
      'log_time' => time(),
      'request_time' => REQUEST_TIME,
      'type' => $type,
      'message' => $message,
      'variables' => serialize($variables),
      'severity' => $severity,