Hide them from where? If you mean the main forum page, then no. If you use the sidebar instead, the categories can be expanded and collapsed, and there is also a Greasemonkey/Tampermonkey script that lets you add your own custom sidebar.
I do wish from the main page I could just have like, 5 or 6 subforums so I don't have to scroll down past everything. Maybe I'll look into this side-bar thingie...
