Assumption: You want to send an email via the news forum to your students (e.g. the lecture tomorrow morning will be cancelled). Another teacher accidentally hided the news forum which you don't realize. Now you perform the following steps:

• Post a new forum entry
• View the message that describes that post will be send via email in 30 Minutes (you expect everything should be fine)
• Your students hate you as they did not receive a message. (Email is send only to other teachers or to other people who have the right to view hidden entries)

I propose the change of the feedback text the poster receives, in case the forum is hidden. Something like:

"Your post was successfully added.
WARNING - This forum is hidden. Only course members who have the right to view hidden enries will receive this message. -
You have 30 mins to edit it if you want to make any changes.
(Continue)"

This will improve usability and still work for people who use hidden forums e.g. to communicate only between teachers.