This is a fairly big problem for my Moodle installations as well.
With assignments you can still go in and open the eyeball after you have hidden a topic. The problem we are running into is with quizzes now that they no longer have eyeballs to hide/show the grades in the gradebook, everything depends on the review options.
We have the review options, in the quiz, set to show the grades in the gradebook but once the topic is hidden there is nothing you can do aside from go into the mdl_grade_items database and manually change the hidden field to 0 for the specific grade item. This doesn't scale well and is impractical for non technical / non IT users.