[Jeir]

Potty training is possible. All but my current Syrian has learned to use just a sand pit to potty. My current one almost always goes in his wheel, and usually in his house as well.

You don't need to worry about them getting sick. Dwarf hamsters always pee in their wheels and are fine. I would recommend only cleaning the wheel once or twice a week, though, as over cleaning can just make your hamster get upset and pee even more (cleaning makes his scent go away, peeing brings it back).