Disable CKEditor on summary
I solved this for the CKEditor module for Drupal 7 by altering the widget itself using hook_field_widget_WIDGET_TYPE_form_alter():

/**
 * Implements hook_field_widget_WIDGET_TYPE_form_alter().
 * Set the '#wysiwyg'-attribute to false for the summary fields.
 */
function YOURMODULE_field_widget_text_textarea_with_summary_form_alter(&amp;$element, &amp;$form_state, $context) {
  if (isset($element['summary']) &amp;&amp; !isset($element['summary']['#wysiwyg'])) $element['summary']['#wysiwyg'] = false;
}


Hope this helps!