I've had teddy bear hamsters and they did this for fun. The one who laid down and rode helped the other keep the wheel spinning once it slowed down instead of jumping off. If one of them felt threatened or hurt they would have gotten off and hid in the bedding. I don't really see it as animal cruelty if they are doing it themselves for entertainment.
ETA plus, the other jumped out when he was done and went for the food bowl. A hamster in distress has no interest in food.
Re: CHALLENGE
ETA plus, the other jumped out when he was done and went for the food bowl. A hamster in distress has no interest in food.