Posted this answer in the issue @attiks mentioned as well:

The easiest thing to do is to add the states in hook_form_alter() or in hook_form_FORM_ID_alter().

I got Clientside Validation to work on fields within a group, within a field collection.

Here's my code:

    /**
     * Implements hook_form_FORM_ID_alter().
     */
    function fgtest_form_article_node_form_alter(&$form, $form_state) {
      $group = 'group_customgroup';
      $collection_bundle = 'field_my_collection';
      $fields = array_keys($form[$collection_bundle]['und'][0]['#group_children'], $group);
      foreach (element_children($form[$collection_bundle]['und']) as $delta) {
        $collection = &$form[$collection_bundle]['und'][$delta];
        foreach ($fields as $field) {
          $collection[$field]['und'][0]['value']['#states'] = array(
            'required' => array(
              "#edit-field-my-collection-und-{$delta}-field-make-required-und" => array('checked' => TRUE),
            ),
          );
        }
      }
    }

And here's my setup:

**Node Article:**

![snap1][1]

**Field Collection field_my_collection:**

![snap2][2]


  [1]: https://i.sstatic.net/EGs45.png
  [2]: https://i.sstatic.net/3S9JI.png