This is by no means a definitive response... just my best shot.
In general, you will find tandems of a given era will tend to use the same components and technologies that were available for their single-seat counterparts. Therefore, you will find a few tandems built after the Bowden cable was invented in the early 1900's that have used brake rods but mostly for drum brakes. Off hand I want to say some of the English 'touring' tandems with drum brakes produced before WWII still used them, in some cases as part of a cable-drive rod. However, most of the better tandems like the ones being produced in pre- and post-war France used cable-activated rim brakes. Raleigh used rod brakes well into the 1960's on some bikes but I don't believe they put them on any tandems... just can't be sure.