Well. They're wrong. I'll say that until they show original sources that are better than mine. Second of all, the idea that drums require significantly more volume of fluid is ludicrous if they understood the hydraulics.
Tim - you had the right idea. Keep an eye on it, and you'll be fine. When a correct tandem MC isn't available, the aftermarket sells drum-drum MCs under the drum disk part number. The major change is that they remove the little residule pressure valve. I used one of them from early 1990s until this year when I finally got a big-little like its supposed to. If I wasn't putting it on a road course I would have been less concerned. Doing laps has a reputation for eating through pads.