Drupal 7: How to use CKeditor with Rules email
I know this is an old issue but i had the same problem and could not find any answer so i figured it out myself.I thought i will put my findings here maybe it will help others.

Most important is that you should use text_formatted not text_format otherwise rules cannot render the field correct. Second is that you should use a different hook "mymodule_rules_action_info_alter" to change the type of the field. See in the example code how i changed the html body field for the mime mail rule "html email"

function mymodule_rules_action_info_alter(&amp;$actions) {
  $actions['mimemail']['parameter']['body']['type'] = 'text_formatted';
  $actions['mimemail_to_users_of_role']['parameter']['body']['type'] = 'text_formatted';
}