Oh yayz, a rain team. I'll give some tips here.
Politoed
Okay, physically bulky is nice, I use it from time to time as well. Although burning isn't really a priority on physically bulky, so say bye bye to Scald. Surf / Hydro Pump both work well in it's place. Perish Song + Toxic stack also kind of screw with each others's jobs.
Thundurus-T
Well for starters, Volt Absorb is his only available ability :P
Nature can be changed to Modest, and a scarf is a much better item for his stats.
Toxicroak
A nice set. A slightly more bulky alternate could use Black Sludge as an item and Bulk Up > Swords Dance if you want though.
Dragonite
Well, a phazer is always cool, but... you don't exactly have any hazards to give you a reason to phaze :P
Although mixed rain-nite is a nice pokemon. Try this approach.
Dragonite (F) @ Lum Berry
Trait: Multiscale
EVs: 160 HP / 96 Atk / 252 SAtk
Quiet Nature (+SAtk, -Spd)
- Outrage
- Hurricane
- Thunder
- Roost
Even 328 attacking stats. Outrage is 120 BP STAB, Lum berry cures confusion. Hurricane is 120 BP STAB, has a 30% chance to cause confusion, and Thunder is 120 BP coverage. It can get some nice parahax. Add in Roost for some reliable healing and you've got a nice Dragonite.
Ludicolo
As I mentioned earlier, your team is lacking hazards, which in OU... are pretty much essential. Ludicolo is cool and all, but his stats just can't keep up with OU.
So I'm here to recommend a classic.
Ferrothorn@Leftovers
Ability: Iron Barbs
Nature: Careful
EVs: 252 HP / 252 Sp Def / 4 Def
Leech Seed
Spikes
Stealth Rock
Power Whip
Pretty self-explanitory. Leech Seed is great for passing, hazards can be set up. Ferro is super bulky and isn't quite as easily destroyed by fire in rain.
Azumarill
Also out classed for OU, sadly. A simple Gyarados performs much better with fitting stats.
Gyarados@Leftovers
Ability: Moxie
Nature: Adamant
EVs: 4 HP / 252 Atk / 252 Spd
Waterfall
Earthquake
Dragon Dance
Ice Fang
or if you don't like setting up...
Gyarados@Choice Band
Ability: Moxie
Nature: Jolly
EVs: 4 HP / 252 Atk / 252 Spd
Waterfall
Earthquake
Ice Fang
Stone Edge