The situation you describe is one where you shouldn't use them. I mean, unless the pillars are so large that you may as well call them buildings.
Generally you want an occluder to cover as much area as possible. Small ones the width of a pillar are going to be mostly pointless, since props and players on the other side would have to line up with the occluder to be hidden.
Personally I don't use occluders often, since proper areaportal use is going to serve you far better. Those times I have used occluders have almost always been around displacement hills or along the walls of large freestanding func_details like buildings -- those being cases where areaportals wouldn't work and props behind the obscuring features were still being rendered.