It is true! A lot of people boat to the Clemson games. You don't dock right at the stadium but it is just a short walk. I've never done it but my brother has. He said there's no official place to dock though. You have to tie your boat up to a tree or anchor it somehow. My brother said they just stopped at a private dock and went up to the house to ask the people if they could dock there and they said sure. Otherwise if you don't get permission you need to make sure you are not on private property.
Your other options are to dock at the Seneca Marina or the Lake Hartwell Inn but those are not really within walking distance to the stadium. The Seneca Marina phone number is 864.653.8100 and the Lake Hartwell Inn is 864.654.4450.
BrownEyedGirl and axotiger went to Clemson so they may be able to tell you more.
How 'bout them dawgs!