I would want to see that in writing from a modern (as opposed to folk lore) source. This sounds frightfully like one of those old wives tales, and anyone who was affect just didn't do it right. Just like those who float are witches.

Poison ivy/sumac/oak are all blistering agents- think very weak mustard gas.

Is smoking grape vines like smoking tobacco or smoking fish?

No, just cutting a length of vine about 3 inches long and lighting the end like a cigarette. I never inhaled the smoke past my mouth; I reckon just to be cool, however, in college, a buddy of mine and I were with a group cutting wood and we were accused of smoking an illegal substance. We were doing it to keep warm while working.

"... Immunizing yourself from poison ivy in this way is not a far-fetched idea. Your doctor, at your request, will immunize you by injecting you with a series of poison ivy extract. ..."

After a little searching I found an article at this web page that is almost like the one I read about the immunization from. The above quote is from the web page. There is a 'Publisher’s Notice' (disclaimer) and 'References' at the end of the page.

Edit: There is also a couple of treatments in the lower half of the article.

Excomantia
P.S. I've never done it myself, just read it.

When I was runnig a Native American Fire Crew and one of the crew got poison Ivy they striped the bark from a Manzanita tree and boiled it then applyed the Juice to there arms, worked for them. We only carried outher stuff for white eyes.