I could imagine that there are more stress forces put onto the drive train at the moment a paddle impacts the sand and during its travel through the sand but I would say that it will not hurt the bike. I have never herd anyone damaging their bike from this kind of use, other than ripping the mud flap from the wheel well.... I did it. The bikes tend to vibrate excessively from a stand still until you gain some forward momentum but after that you cannot even tell your on a paddle tire. I would not keep from buying one because of this information, people ride with paddle tires all the time without any issues. There is probably some truth to this guys claim but I don't think it is an issue. Besides, what kind of strain does a normal knobby tire have while riding in the roots of a forest, or a SM bike on black top (they do use a cush drive though), or spiked ice racers on the frozen lakes up north??? Just my two cents worth....
Regards,
ps. I have had my Berg at the sand dunes over 15 times in the last three years and have not had any problems whatsoever. Lots of time at the sand drags also pushing the bike hard....