I think you will find that Martyn Farr has dived Cambrian - I saw him at Hidden Earth last year when he described what he found. As you would expect all the chambers are linked at a lower level and there are rails, windlas and usual slate equipment in place although quite a few rails had been stripped out.
With regards to foggy photography remember Cambrian has a live stream running through it and the mine therefore has its own unique humidty you just have to be there at the right times to avoid this - don't ask me when
Mike