Ragdoll Cats are not actually hypoallergenic but since the Ragdoll cat has no undercoat that makes them seem hypoallergenic and people who suffer from pet dander allergies are less allergic to the Ragdoll Cat.
People who are allergic to pet dander will usually not have an allergic reaction to the Ragdoll cat because the Ragdoll cat doesn't put as much cat hair into the air unlike some other cats and animals that shed a lot.
So if you're allergic to other cats and allergic to pet dander then a Ragdoll cat may be a perfect fit for you but there's no guarantee that you won't be allergic to it.