The traction motors will be brushless, and thus have large permanent magnets in the rotors. I can't imagine there would be significant fields from those magnets

The traction motors will be brushless, and thus have large permanent magnets in the rotors. I can't imagine there would be significant fields from those magnets in the cabin, but getting a pacemaker or ICD very close to the motors themselves might well pose a risk, and the manual's warnings are likely present partly for that reason and partly out of fear of liability.