I would think saw dust or wood chips would mold with the humidity. You really don't need anything in there until the chicks start to hatch. make sure not to put anything in there the chicks may think of as food. They will learn to eat that instead of the stuff they are supposed to be eating.
Are you using a comercial incubator or a home made one? Which ever don't add no type of bedding material in incubator.Naturaly hatched chick's by hen's will follow the mama's lead on food and water even though they are hatched in hay straw/grass or shaving's in nest box.Artificaly brooded chick's need a different type of brooding when hatched.