You can ski, but pulling a tube is never a good idea, the tube puts way more stress on a tower (and boat where tower attaches) due to the surface area with the water.
i've let women slalom from the tower. don't think i'd let a dude, esp if he was a really good skier. i don't like burning the gas to go that fast anyway though.
Wakeboard, Kneeboard, and small one person tube with a small child less than 100 pounds are the only things we pull from the tower. Ski and other tubes from the transom hook.
this summer we had a guy with a small 17' boat with a tower pullin a tube. he flipped his boat over when he was turning. so i would say its a no go. not sure what kind of tube he had, or how many people he was pullin, but im not going to chance it.
I read the warning labels on a Monster Tower, a stock tower on a Mastercraft x-30 and a Centurion, they all say not to Tube behind a tower, I read about a girl dying a few years back when the tower ripped off and hit her, she was sitting in the rear of the boat while dad was towing her kid brother. It's called a wakeboard tower for a reason!