The torque pulling a good slalom water skier is huge and will pull the back end of a 5000 pound boat going 32 mph from side to side even with a 300 hp engine pushing it (that is why a good ski boat has the ski pylon mounted in the center of the boat). Pulling the large tubes with four or five passengers may even have greater torque. Based on my experience, I can not imagine why you could not tie to the pylon if it is properly installed. You might have to be observant of too much slack and what it does if it drops down along side your outboard. Probably want to make sure it doesn't get hung up somewhere it shouldn't if it goes slack.
