can gobies, dartfish and firefish live in gravel?

as the tittle says can gobies, dartfish and firefish live in gravel? or should it be sand?

i have a dart fish and a firefis that lives in a hole between the sand bed and the rock work, and am thinking of getting a gobie. at the same time am thinking of switching from sand to gravel sense they are easier to be cleaned, so what do u guys thing?