How to theme the edit page of a form and retrieve $form variable from the hook_form_alter into the template for theming purposes?
Try something like this:

function hook_theme() {
  return array(
    'custom_content_type_a_node_form' =&gt; array(
      'render element' =&gt; 'form',
    );
  );
}

function THEMENAME_custom_content_type_a_node_form($variables) {
  dpm($variables);
}