I have not done any of the overnight trails in Fall Creek Falls themselves, but there are a lot of good trails in that same area.
Savage Gulf has lots of great trails for scouts. I recommend the North Rim-North Plateau loop or the Collins Gulf loop if you are looking for something really easy, or a North Rim-South Rim loop if you don't mind something a little more difficult.
Virgin Falls, though only 8 miles round trip, is a great place for scouts, and is a very interesting place.
Fiery Gizzard Trail is a great trail in the south Cumberland area that is full of rugged beauty.