Technically, he's a channeler and uses a method of energy healing similar to Chi Gung. In energy healing modalities such as Reiki, the healer/channeler doesn't "take on" the illness themselves but puts it outside of themselves. A complementary technique that is used in Reiki and other energy healing modalities is called "psychic surgery" where blockages and illnesses are energetically removed.
However... there is also a Native American myth (and I think it may appear in other mythologies) about Sin-Eaters who devour the sin and illness of others and take it on themselves, but the illness, while still active, won't necessarily kill the Eater. They live with it and continue collecting more and more of these until they can't survive anymore or they kill themselves or are killed. I've heard a few different versions (started off investigating it from an X-Files episode, interestingly enough). Might wanna look into it?
BTW, I'm a Reiki Master/Teacher, so if you have any more questions...