Drupal_add_js is not working inside hook submit
You should do this with #attached.

Like,

if (!empty($form_state['values'])) {
  $form['#attached']['css'] = array(
    drupal_get_path('module', 'ajax_example') . '/ajax_example.css',
  );
  $form['#attached']['js'] = array(
    drupal_get_path('module', 'ajax_example') . '/ajax_example.js',
  );
}