Halfway correct. If the vehicle is registered as an RV, you are correct - you do not need a medical/CDL. But as soon as the vehicle is used for commerce, then it legally cannot be registered as an RV, and needs to be registered as a commercial vehicle and the driver needs to be licenced as such. Even if the vehicle is clearly a motorhome, it needs to be registered as commercial if it is involved in the money making process.
Case in point:
Double Eagle makes sleepers for semis that have all the comforts of home, including built in plumbing. Legally, they could be registered as an RV, if it was used for personal recreation. But since they're used to make money, they fall into the commercial category.
It doesn't matter what the vehicle actually is; the intended use is what determines how it should be registered and how the driver is licenced.