I very much doubt that the Force(especially the dark side of the Force) would grant that kind of immunity. In all likelihood, Pinhead's chains would shred right through any Force barriers that Vader could manifest.
...But even IF Vader could block them initially, he can still only keep himself shielded for so long(especially if his shielding is constantly getting bombarded by attacks.) Eventually he would tire and Pinhead would rip him into shreds.
"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."