Let's say, that Pokémon's EVs are maxed out, so is EV bonus afflict stats:
-when leveled up during battle
-when leveled up in Daycare
-when leveled up by Rare Candy
But what about leveling up in Pokéwalker and other ways?
I'm not sure if I fully understood your question, but I think you asked if Pokemon still are affected by EVs when they level up via the Pokewalker. I apologize if I misunderstood, though. :P
The Pokewalker doesn't have enough system function and memory to wield the features of EV mechanics, so when a Pokemon levels up, then the level-up stat gains would likely be set to a default gain.
I think it still would work even on the pokewalker. I don't think that it thinks of the stats untill it go's back to the game. For all of the rest of them I am sure that it will still give you the EVs. Rare candies are only bad because if you only use them then you won't have any EVs.