I talked to some of the locals up there last year, and it sounds like the outfitters (the put-in and take out are outfitter-owned) have this rule in place to eliminate other outfitters from using their property / i.e. pirate trips.
I would contact OWL and let them know what you're planning on doing, and my guess is that they would be OK with this (contact one of the owners / managers over e-mail, rather than calling the reception line). Or you could just go up and put on --- if you're planning on just taking your cat and not a large flotilla I don't think anybody would notice.
I would also check with the boatwerks board and see what kind of response you get. http://www.boatwerks.net/boater-board?f=1&sid=4d98f7056521af641406676fd917b0b3
I am curious as well --- my SO would love to take her Thrillseeker down. I asked around last summer, and the above was what I was told. Beautiful place!