Cameras are not allowed on the ride, unless of course it's a small one that can fit securely in your pocket(this works well with cargo shorts that have either zip or buttoned pockets). A DSLR would not be allowed on the ride with you, and a TM will make you take the camera down to a locker if they saw it when you tried to ride. If you want to take pictures throughout the FJ line, then after riding take the Castle Tour, it is a separate line where you can take your time wandering through the castle taking all the pictures you want. The Castle Tour is the best way to get some amazing shots and without having to worry at all about holding up the ride line or the safety of your camera.
As for having someone wait in line while someone else does the locker, then sure that's ok if you want don't mind riding separately. But having someone push through the line to meet up with you would probably cause more issues than it would solve unless the ride is a walkon. For one it could upset people, but also many parts of the FJ queue are dark and get congested fast, there is also stairs and there are many twists and turns that could make it difficult and uncomfortable for someone to meet up with someone further into the line.