Yes. If the slab is about half the width of the router table.
I've done it by attaching straight strips of wood to the opposite edges of the slab to create sled-like runners. The runners have to be co-planar. Then move the slab over slightly protruding router bit making sure not to hit the runner. You can use fence as a guide. It's fast an easy method for surfacing small pieces such as cutting boards etc.