In a vacuum, the proposed spread for Azumarill optimizes its defenses given 252 EVs; this is an objective, mathematical fact. Certain calculated damages may be the same due to rounding. Of course, it may be beneficial to invest EVs elsewhere, but for any defensive spread of 252 EVs, the spread listed on the site is suboptimal.
However, considering environmental conditions, the spread listed on the site is better because 404 HP takes less damage from Stealth Rock than 400 HP on the order of one part in one hundred, while the proposed spread is defensively superior on the order of one part in one thousand. So the spread onsite should stay, but not for the reason RT. gave.