The use of a dog bone adapter is primarily for plugging in an RV not an alliance. When you plug in your 20/30 dog bone into your house, 20 amps is applied to you 30 amp cord and is run to your 30 amp main breaker in your RV. The 20 amp breaker in you house just became your RV main breaker. You will have full access to anything in your RV as long as the total amperage used does not exceed 20 amps.
You really would not have a need to go 30/20. If you were doing that then yes you would leave what ever is plugged in exposed to a 30 amp breaker.
The flip side is if you use a 50/30 adaptor. You can plug your 30 amp RV into a 50 amp plug BUT you are protected my the 30 amp main breaker in your RV. Only 1 hot leg of the 240 50 amp service is applied to your Rv.
If you are so inclined you can install a 20 amp GFI device before the appliance. I am an electrician but I would not be bothered to do that. But that is just me. Camp ground usually have a 20 amp GFI outlet available so I don't see the need to adapt down 30/20.