I don't think I have ever seen jet ski's...but at Fort Wilderness you can rent little power boats. My brother did it and really liked it. Just don't try anything crazy because the guards in the whaler boats will come and get you!
There are no Jet Skis, but they have the little Sea Raycers. Keep in mind that a newer rule with the Sea Raycers is that at certain resorts, someone in the boat must have a valid drivers license.