No they aren't free to write what they want. They are specifically instructed to omit certain items.
I assume you've read one of these confidentiality agreements then, or can provide a link to an article documenting these restrictions that film critics must follow? I've never heard anything along these lines from professional film critics, and I would be surprised if they existed.
But it would certainly be intriguing if your claim was true, and I'd be interested in reading more about it if you can find something backing it up.
On the subject of corruption among film reviewers, if it were as bad as you suggest, why would Sony go to the effort to invent an imaginary film critic
? Wouldn't influencing actual film critics just be easier?