Certain types of tubes will definitely exert more force on the tower than a wakeboarder.
The amount of force a wakeboarder will exhibit during wakeboarding will essentially be equal to the maximum grip strength the person has. There are exceptions of course, given that when the line goes slack the sudden force of the rope being taken up will create essentially an impact force on the tower.
As far as tubes, will a small tube exert more force than a wakeboarder? Probably not. But a large tube, with multiple people, during times when the rope slack is taken up OR especially if the front of the tube were to become submerged and drag in the water, that force will definitely more than a wakeboarder, and could exceed the design forces of the tower.
The height of the tower definitely creates a very large moment at the base of the tower.
Ultimately it's your boat, do as you please. I would never tow a tube from the tower.