No. They should be fed on a plate or bowl of some sort. I use tera cotta plant saucers or flat butter tub lids.
A small amount of accidental substrate ingestion should not be a big deal. But if they are eating a substantial amount of it every day, it could be bad.
Try using a piece of tile or a plant saucer to reduce accidental ingestion. I have to put Ruby's food in the back corner of the tile otherwise she pushes it off and eats in the dirt.