Grass was drafted into the Waffen SS as a 17 year old recruit at the end of the war. his choice was to join or be a dead man. Incidentally, the Waffen SS had nothing to do with concentration camps. That was the responsibility of the political branch of the SS.
About 2,000 demonstrators protest 'occupation policy and fascist settlers' in Nazareth (Haaretz)
from the article: Interior Minister declares Gunter Grass persona non grata in Israel