Only nine states have outlawed red light cameras. Your "many" statement you made earlier is, in fact, just "some."

The sixth amendment challenge has been proposed several times, but very few of the actual rulings I can find contained anyone successfully using this as an argument. One for instance is The People v. Khaled in California where the camera operators were not available for cross-examination. All the state has to do is provide their witnesses and the sixth challenge goes out the window.

Insofar as red light camera schemes have been declared unconstitutional in state courts, this is most often because the scheme in question exceeded the authority granted to cities and municipalities, which tried to go over the heads of their superseding states. You can call this a win since they were indeed declared "unconstitutional," but not for the reason you specified. The US Supreme Court has also been silent on the sixth amendment argument.

So, fixed that for you.