I have hidden our forum to guests using a guest conditional statement in forum_list, but would like to allow guest viewing of a single forum that we use as a public blog.
Hmm, not sure. I guess because that's how we used to do it on XF1.1. I'm a little out of the loop.
Instead I used a guest conditional statement to hide the sidebar in forum_list, and set never permissions for viewing most of the category nodes, allowing the one forum I wanted. Works a treat.