No, I've had several students answer "I don't know" to every question on the final exam. (About one every two or three years.) Without exception, they got a 25% on the exam and an F in the class.

Other theory instructors at Illinois do put limits on their IDK policy, like "at most 10% of the total points", or "for at most one question", or "not in my class". So far I've stuck to my guns.