Yes, some owners are OK with renting their RV in the winter.
For renting RVs in or from areas with below freezing temperatures:
Bear in mind that if you are planning a winter camping, due to freezing temperatures, you will not be able to use the water, toilets or showers, so make sure that the camping ground you selected has those amenities.
If you are planning to take the RV to warmer areas in the US, It would be best to work with the owner directly to get specific instructions on how to handle the unit while it is moving from cold to warm climate and vice versa. You will need to follow the instructions thoroughly to avoid internal damages in the RV caused by freezing liquids.