You mean in their offspring or against each other? Because the last time I checked you can hold Pikachu without it shocking you and Mudkip isn't entirely made up of water. As for offspring, if you bring it down to genetics it could work. Chinchou and Lanturn are electric/water pokemon. Wouldn't they shock themselves in the sea?
It's nice to know my work is creating such lovely ideas in people’s heads. Then again can you imagine if they were christened? The vicar would put water on the little Pikakip’s head and then be electrocuted in front of all the baby’s friends and family, again a lovely mental image.