Ditto isn't hard countering azumarill anytime soon. he can revenge azu but can't come in on anything not named belly drum.Anyway, back to the BellyAzu matter. People run Scizor, Ferrothorn, Ditto, and now Talonflame all the time. They don't really use them for checking on a BellyAzu in particular. Ditto is a hard counter. Scizor can check many other threats along with BellyAzu. Talonflame is a fine sweeper with priorities. Ferrothorn is one hell of a lead. They serve many different purposes, which include checking on that Azu if the enemy has one.
Ferrothorn's lead skills are irrelevant (if you are leading with ferro chances are it is going to be weakened by the time it faces azu).
All of you saying BellyJet is bad are almost assuming azu comes in turn one and belly drums. BellyJet is strictly a late game sweeper, the only other role you should make azu do is revenge kill some water weak mons (Blaziken, tyranitar, excadrill, volcarona, mamoswine), and physically weak pokemon (Gengar, alakazam, smeargle), while smacking a predicted switch in hard with either waterfall or play rough.
As for EVs, the easter bunny will at least need to outspeed Jellicent (84 spe for min speed) by the time PokéBank comes out.