I welded for several years, got shocked a lot of times from welding while standing in water and other liquids and never heard of any one getting messed up blood from it. Then again, lots of things I never heard of but I would think that if it was a problem, our diligent first aid/safety gurus would make the welders be tested for it which we dont do at my company and we have one of the most diligent safety staff in the world. When welding while standing in the water, get some rubber boots, dont lean on the pipe or what ever you are welding when changing rods, keep a good well insulated electrode holder on your stinger and most important, use dry gloves. Even if you get tingled, it isnt like grabbing a 110V current, although it does bite a bit. As long as you keep your rods dry, whatever you are welding dry and most important, keep the water off your hood you are ok. A few drops on the dark lens and you will be guessing which arc is the real one. As for actually welding in the rain while wearing a slicker suit, thats not going to happen on my jobs, at least not if I know about it being as I am a Quality Manager. The rods better be in a hot box and powered up, the rain shelter / wind break better be covering up the work area and the welder better be qualified. NOW he may be in the mud on his back with water running down his collar, but that weld and electrodes better be dry.
