How do I make the nodes referenced by organic group content also be OG content?
Here is the solution I've come up with. 

It works, but might not be the most elegant solution. I didn't think that this would matter too much, since it's only being called on node save, but I'm open for comments and suggestions.

/**
 * Ensure that referenced nodes belong to the same organic group
 * 
 */
function MODULE_node_presave($node) {

  if ($node-&gt;type == NODE_TYPE) {

    $og = og_get_entity_groups('node', $node);
    $nids = get_referenced_nodes($node);

    foreach($nids as $nid){

      $child_node = node_load($nid);

      //Set the values
      $values = array(
        'entity_type' =&gt; 'node',
        'entity' =&gt; $child_node,
        'state' =&gt; OG_STATE_ACTIVE,
      );  

      //Add this node to the group
      $gid = array_values($og['node']);
      $result = og_group('node', $gid[0], $values);

    }    
  }
}


/**
 * Helper function - get all node reference fields of a node
 * @param $master_nid - the node id of the referencing node
 */ 
function get_referenced_nodes($master_node) {

  $fields = field_info_instances('node', $master_node-&gt;type);

  $items = array();

  foreach($fields as $field){

    if($field['widget']['module'] == 'inline_entity_form'){
      // Get the node reference items for this field
      $items[] = field_get_items('node', $master_node, $field['field_name']);

    }

  }

  // Loop through and grab the nids
  foreach ($items as $field) {
    foreach($field as $target){
      $nids[] = $target['target_id'];
    }
  }

  return $nids;

}