vbulletin auth external page - is this enough for admin area?

[forcerm]

I have built my website around vbulletin, i use the include globals.php hack so that i can work with vb on external pages.

I also have an admin area to go with this, now rather than create a separate login to secure this i decided to limit admin area access to the vbulletin admin usergroup.

PHP Code:

       if($this->vbulletin->getUserGroupId()!="6")
               redirect(base_url());     

        //admin code here... 


So this is saying, if usergroup isn't 6, then redirect to the base_url (home) or continue...

This does work, but since it's not actually checking if the user is logged in, rather it's just looking for a usergroup id... is it secure enough?

If the user is not logged in, what will it return? NULL? 0?