A forced confession while been shot arrows by a maniac that killed or injured several people?
Yes, that is going to hold in court (?).
Actually if a cop had forced the confession it's not admissible but the police getting the confession from a non police third party often is.
People just assume the police can't use that kind of information.
Admissible or not (and I question its admissibility as well since it was given under duress), no defense attorney worth his or her salt wouldn't tear that confession to shreds in court. And big time corporate crime boss Captain Kelly from BSG guy doesn't strike me as the type to hire a bargain basement defense team.
It's all a moot point in these superhero stories, though, where due process and proper legal procedures fly out the window until the moment you want to make a story about them so the bad guy can get off (see: Lex Luthor in Superman Returns
for one example).