[Razor]

Hello!
Bathing in the sand is something that kicks in by instinct. It's usually the dwarfs that love bathing in the sand, whereas syrians just prefer them as toilet. Hamsters in any case tend to groom themselves often, much like a cat would. So as long as you see that s/he is grooming themselves, don't worry about it. And of course, if you have a long haired syrian, you have to help out grooming the skirt.
While on the same note, as long their fur is smooth and has a shine to it, they're grooming themselves alright. It would be of concern of the fur starts appearing matted and unkempt.