So, your staff forums are the forums where your staff can just chill and get away from the rest of the forums. Do you find that this makes that section more active? Is it this way on your forum? How many posts does your staff forum have?
I have a staff forum on my forum & in it i have a sub-forum for each staff position, mods, reviewers & achievement writers. I didnt have the staff forum from the start so my other forums are still more active than the staff one, but it is still active and maybe catch up in the future
It actually depends on the genre of the forum. If you own a webmaster community, with no many groups, then one staff section is good. If you own a promotion forum, with many groups, then you need to have section for each group.