
But hams like making a grass/tissue nest where they sleep.

I understand your hams merajuk. My robos used to be like that. Whenever I try to take out the sand they will all jump into the bowl at the same time. They'll get used to it. You just have to keep doing this until it's habitual for them to do their business in the toilet sand.
I don't think the rumor applies although you may notice that female hams will make several nests in several locations when she is pregnant. Whenever one of my hams get pregnant, she makes nests all over the place and fights with other robos that infringe her nest (other than her male).
To be safe, just count the days until she gives birth. If she's pregnant she'll get rounder, not exactly fatter. Remember to give bigger portions of protein ok?
@bruised: Your robo is using the bathing sand to do what it's made for. Your robo is bathing by flipping on its back. If your robo doesn't flip anywhere else then it's fine.
The thing about robos is, they LOVE to pee in the wheel as much as they love the wheel. There's no point in trying to stop it because it won't. It's a habit shared by most robos.
I recall only chipsi classic and chipsi super are ok. Others are not so. Pet Wonderlad sells Chipsi classic at RM 26 for the big pack I think. You can try there. If there are no side effects (bleeding nose, etc etc) then you use finish that medium pack first. Then buy proper bedding ok? Long exposure to bad bedding has bad effects to their general health.
@nezu: The research never stops right?

Learning is a life long experience. I was researching calcium for suggies and piggies. It was stuck in my head till I reply here.