Disney no longer allows third-party photographers in the park (as of 2009/2010), unless they are shooting a Disney Fairytale Wedding and have permission (as of 2013).
Now, that's not saying you couldn't go in and do it behind Disney's back. But reputable photographers in Orlando who shoot many Disney Weddings and family sessions will not risk getting caught in the park because their future business depends on it (if they get caught, they'll be blacklisted from future events). They will, however, shoot at any of the Disney resorts, Downtown Disney, or Disney's Boardwalk.
If you are set on going in the parks, you could hire a photographer who doesn't shoot much at Disney.