Torque is torque. It dose not matter if the torque is in torque tube or an open drive shaft. The forces will be the same-vertical on the frame. If you are doing a wheelie you have no force on the front wheels to counter react the torque this could twist the frame.
I guess I have to disagree with a couple your points. Maybe others can chime in here to comment.
"Torque is Torque." Right, except torque is not vertical. It is a twisting force. The only time you can say it is vertical is when it is transferred to the rear axle and then the twisting force is at right angles to the frame and the
effect will be to push up on the frame by way of the springs or radius rods.
With a torque tube, there are solid connections between the engine, driveshaft, rear axle and wishbone. The engine torque or twisting force will be contained within that solid assembly until it does its work at the rear wheels.
With an open driveshaft there is no solid housing between the engine, driveshaft and rear axle. There are two open universal joints. The twisting force is transferred along the moving driveline but not along any solid housing.
Therefore, the engine is allowed to twist around the crankshaft and is only limited by the cushioned motor mounts. If there are solid rear motor mounts then the force is effectively transferred to the frame at that point. That force in turn will twist the frame at the front half. The effect will be lessened by a stiff frame, springs or shocks. There will be no vertical lift except that caused by the rear wheels.
For example, put an engine on the floor and start it up. Rev it hard. Get out of the way! Another example, hundreds of photos have been taken of dragsters coming off the line where the front end is off the ground but also twisting. The twisting is due to the torque of the engine.