Haha, not a bad idea, but you're going to want to stay away from pure water types and hint more towards dual types for more diversity.
Politoed
I'd go for a different EV spread of 252 HP / 252 Sp Def / 4 Def on him. Politoed really works better as a bulky pokemon, and it also fits your moveset.
Vaporeon
Vaporeon isn't going to do much more than Politoed can, so I'd aim for a Rotom-W in this slot to have a nice scout and add more type diversity.
Rotom-W@Choice Scarf
Trait:Levitate
Nature:Modest
EVs: 252 Sp Atk / 252 Spd / 4 HP
Volt Switch
Hydro Pump
HP Ice
Trick / Thunder
Volt switch will let you scout and get damage on good switches, while hydro pump is used for rain boosted STAB. Thunder is a possible secondary STAB move that can be interchanged with Trick, which can break walls. HP ice is nice coverage.
Basculin
I would swap him with either Gyarados or Sharpedo depending on what you're looking for.
Gyarados@Lum Berry
Trait: Moxie
Nature: Adamant
EVs: 252 Atk / 252 Spd / 4 HP
Waterfall
Ice fang
Dragon Dance
Earthquake
Sharpedo@Life orb
Trait: Speed boost
Nature: Adamant
EVs: 252 Atk / 252 Spd / 4 HP
Waterfall
Crunch
Aqua Jet
Ice fang
Swampert
Superpower and Curse together will usually lead you to certain death, so i'd replace superpower with Brick Break. Lefties is a nice item for swamp as well.
Poliwrath
Nice type choice, but another special attack would work well here, and swift swim is banned in general competitive play. Keldeo makes an amazing replacement, though.
Keldeo@Life orb
Trait: Justified
Nature: Timid
EVs: 252 Sp atk / 4 Sp def / 252 Spd
Hydro Pump
Secret Sword
HP Electric
Icy Wind
Whiscash
Yes! A fellow Whiscash lover! Use him well.
If you want to take down Dragonite with Keldeo's Icy wind, you can add S-rock Carracosta in this slot.