I've never seen any of O'Keefe's commentary on Dieppe, but I'd question the level of confidence in any intelligence that the Germans had a 4 rotor Enigma machine available for the picking at Dieppe.
There may have been more accessible and less heavily defended locations where a small hit and run commando raid might have had a better chance of picking one off.
It's a sure thing that such a sensitive encoding/communication device would have been well to the rear and heavily protected at Dieppe, and that adequate time would have been available to the Germans to either remove or destroy it to prevent its capture. There's been a lot of after the fact justifications for the Dieppe raid over the years, and this may just be the latest.