It is decidedly true that a large number of Germans did so after the war. It is less true that a large number of Waffen-SS veterans did so. Certainly some did, but the French made at least attempts to weed out veterans of the SS, such as by refusing entry to men bearing the blood-type tattoo indicative of membership. Not that some didn't manage to join surreptitiously, but it wasn't rife them them as some popular narratives allege. I've written about this in more depth in this older response which may be of interest.