Hullo, I've tried to reproduce this internally (I work for Smoothwall) and not seen the page blocked by that category. When I visit it I have traffic put into education and reference. As a suggestion, create another category and add the domain (and also the feeder domains for the site content, I'm afraid) to that category and then make it a custom allowed site. It'll mean a fair bit of watching the logs for those feeder sites but that will allow you to view the site.
I hope this helps, I'm sure you've already given this a try.
Kind regards,
Nick