There's an old thread about descending Ventoux that's quite interesting:
http://www.bikeforums.net/tandem-cyc...t-ventoux.html

I recall only one mention of a rim-braked tandem w/o drum. It had no problems, while all the discs had troubles. Older tech, but maybe something the OP might want to peruse. When we tour, we put on our spare rear with the Arai.