Do you need to use the Disqus plugin? ie are you synchronising with WordPress comments (own your own comments etc). If not, it’s easier and quicker to remove the plugin and just edit the comments.php file (the actual file depends on your theme but this is the most likely one).
This answer has the Disqus javascript code and you can get the Facebook code from Facebook’s Developer Site, and then simply do an if-else with in_category(..) as the condition.