No! The most hazardous part is the potential for slipping on the autumn leaf fall on the way back down the access paths. It gets 'damp', as in a few trickles from the roof and the odd minor flow down the main passage. There isn't any stream in the system.
There is a duck near the bottom that leads into a lower section still, and I'm sure there is a 'sump' at the very bottom, but only in the sense of a water-collection hole rather than diveable passage, but it is very high up so it's well-drained naturally really. I'm sure some ancient sough was responsible for keeping it all dry - most likely Wragg Sough, started in 1680. The history, geology and archaeology of the workings along Coalpit Rake are discussed at length (with a modern survey) in the PDMHS Bulletin 'Metal Mines Through Time', Vol 17, No.3.