Sgt. Schultz was *not* a double agent. He was always loyal to the Germans, but he was also *very* fond of the POWs.
Here's why the theory is false:
* His characterization: Schultz was portrayed as a bumbling, easily-bribed guard. While he often looked the other way at the POWs' antics, it was out of self-preservation and a desire for peace and quiet, not out of any allegiance to the Allied cause.
* The show's tone: Hogan's Heroes was a lighthearted comedy, not a serious espionage drama. The focus was on the prisoners' clever escapes and the humor of their interactions with Schultz and other German guards.
* No evidence: There is no evidence within the show's storyline to support the idea that Schultz was secretly helping the prisoners.
While it's a fun thought, the idea of Schultz being a double agent is just a popular fan theory and not part of the show's canon.