Ummmmm, NO.
Wouldn't even think about it.
And, it has nothing to do with concern about druggie relative.
I would not do it because I do not think it would be in the best interest of the child.
If a kid is old enough to make their own decisions, then that should be up to the kid. Otherwise, no way, ever. A younger child could only be traumatized by making such a big deal out of something like this. And, really what is an older kid going to gain????
Either the kid is smart and knows that these kinds of things are choices that have consequences, or not. Many teens have a sense of immortality and invincibility, no matter what they have seen.
My DS recently lost his Grandpa (FIL) due to lung cancer (former smoker). DS is young, but he does understand, from my DH's comments, that cigarettes are not good for you and can make you sick. But, to drag a child into a hospital like some kind of field trip??? Could be a very misguided idea.