I think there is a difference between dangerous conditions and wet conditions, we have had a ring stopped once or twice when it became dangerous due to excessive mud etc, and obviously contact equipment etc comes into play in these situations, wouldnt risk seesaws etc in mad weather, but it is no less risky to train in the rain that it is when its dry, agility is a pretty low risk sport and I think you would struggle to find handlers that would ever put winning a class before their dogs safety.