The soil of bonsai planted on stones is normally covered with moss
Yes, but
to prevent washing away when water is applied.
no. The moss is there for decoration, to hide the wires and the walls, and
a bonsai is defined as a "plant in a pot."
no, and
bonsai need a granular open substrate with good drainage
this would fall apart easily when watering, regardless the moss, when used this way.