Here's the thing and this is just IMO.
If you are going to run a slick with a tube SCREW THE BEADS! You are asking for trouble if you don't because if you spin the tire on the rim you WILL pull the valve stem inside the rim and end up in the wall.
If you are running a slick with out a tube (which is not safe in my book) its up to you on running screws or not.
Again IMO I would always run a tube when using slicks.