This mod does put them in the <head> area of the page, at least on the default vBulletin styles.
If you have Facebook enabled on your site the mod looks for the text
Code:
<meta property="og:type" content="article" />
which is in the <head> area when Facebook integration is enabled and adds the extra og:image tags below it.
If the Facebook platform is not enabled it looks for
Code:
<!--[if IE]></base><![endif]-->
and uses that instead. In both cases the code remains inside the <head> section of the source code.