As an inelegant solution, I just added another conditional: (using membergroupids instead of usergroupid)
HTML Code:
<!-- START Side Tab Secondary -->
<vb:if condition="in_array($bbuserinfo[membergroupids], array(13))">
<a id="floating_link" href="http://somethingorother.com" target="_blank">Click Me</a>
</vb:if>
<!-- END Side Tab -->
There has got to be a better way though. Suggestions?