It’s been awhile since I stayed there but I think no. The cabins sit on a foundation and I believe there is a deck attached. I don’t recall there being a concrete slab. Could be wrong as I said it was several years ago.
Well there is the slab that the car can park on in front of the cabin. That can probably be chalked. Disney doesn't care if guests decorate their driveways as it will wash off with the next rain.
Decorating the sites or drives with chalk is a nice touch IMO.