No, not exactly. The _links hook requires a full on link. (I actually got this code from one of BOPs mods.)
Try this:
Code:
$template_hook['custom_css_links'] .= '<link rel="stylesheet" type="text/css" href="clientscript/vbulletin_css/style' . str_pad($style['styleid'], 5, '0', STR_PAD_LEFT) . $vbulletin->stylevars['textdirection']['string'][0] . '/ct_thread.css" />';
$template_hook['custom_css_list'] .= ',ct_thread.css';