Is there any way you can hide a forum from the forum index? Basically, I'd want my staff forum not to show on the index- but I'm adding a link to them on the nav bar. 

ACP->Community->Forums->Forum drop-down item->Permissions

Can this work for you?

what I would do also  is just  remove those categories   (make them not viewable) for all usergroups, 

(at the "groups"  setting)

except for the usergroups that you want them to see

i.e. moderators, administrators. etc. 

This way you can have moderators see only a certain sub forum,  etc, others see another

We worked our previous  forum software like this for many years, and it was very convenient, 

but I ll try what you are saying also. 

 I would be curious from other users (moderators for example if they found this or the other method better or not.    

 (the link in the navbar vs the hidden section at the end part of forum   )

I dont even know how to put a link in the navbar so I will probably go figure that out as next step :-) 

 

You can easily add a new tab in navbar from Menu Manager (don't miss to hit the "Publish this menu"), then set all the appropriate permissions you want on forums and you're done.