How can I obtain the "latest" vid when on Revisioning's "View latest" tab?
I dug into the Revisioning module to see how they are doing the check and adapted it for use in a helper function in my module. I first load the node using menu_get_object() and then call the following:

function _get_correct_revision($node) {
  if (module_exists('revisioning')) {
    if (_revisioning_load_op($node, 'view') == REVISIONING_LOAD_LATEST) {
      $vid_to_load = revisioning_get_latest_revision_id($node-&gt;nid);
      $node = node_load($node-&gt;nid, $vid_to_load);
    }
  }
  return $node-&gt;vid;
}