Correct.
Here, as an example, is the head JS from Google DFP ...
HTML:
<script type='text/javascript'>
var googletag = googletag || {};
googletag.cmd = googletag.cmd || [];
(function() {
var gads = document.createElement('script');
gads.async = true;
gads.type = 'text/javascript';
var useSSL = 'https:' == document.location.protocol;
gads.src = (useSSL ? 'https:' : 'http:') +
'//www.googletagservices.com/tag/js/gpt.js';
var node = document.getElementsByTagName('script')[0];
node.parentNode.insertBefore(gads, node);
})();
</script>
<script type='text/javascript'>
googletag.cmd.push(function() {
googletag.defineSlot('/2799641/Sidebar', [142, 180], 'div-gpt-ad-1329816300296-0').addService(googletag.pubads());
googletag.defineSlot('/2799641/Text', [234, 60], 'div-gpt-ad-1329816300296-1').addService(googletag.pubads());
googletag.defineSlot('/2799641/TopBanner', [728, 90], 'div-gpt-ad-1329816300296-2').addService(googletag.pubads());
googletag.pubads().enableSingleRequest();
googletag.enableServices();
});
</script>
The three lines near the bottom, beginning "googletag.defineSlot("... are the unique part, and you could have between 1 and xx lines here depending upon how much inventory/positions you have defined within DFP.
Google DFP has 3 delivery code types/methods - syncronous, asyncronous, and ad manager (old type). Each type/method has different head JS, but for the purposes of your Ad Manager and xenForo you'd probably only want to support one method, with asynchronous being the better/fastest