lib/xmlrpc/php/openads-xmlrpc.inc.php is the script used to call from php to get a XML-RPC ad
this is a sample from my current server....
<?php
/* <!-- Revive Adserver XML-RPC Tag - Generated with Revive Adserver v4.1.3 --> */
//ini_set('include_path', '.:/usr/local/lib');
require 'openads-xmlrpc.inc.php';
if (!isset($OA_context)) $OA_context = array();
$oaXmlRpc = new OA_XmlRpc('ads.mr.com', '/www/delivery/axmlrpc.php', 80, false, 15);
$adArray = $oaXmlRpc->view('zone:1', 0, '', '', 0, $OA_context, '');
echo $adArray['html'];
?>
so if you can mimic that class, you should be able to get and deliver an xml-rpc ad.
if you want to do management tasks you will need to utilize or reverse engineer the lib/xmlrpc/php/openads-api-xmlrpc.inc.php file.
there is java classes available as well... https://github.com/revive-adserver/revive-adserver/tree/master/lib/xmlrpc