There is (at least) one way to estimate your EVs in Gen 4. You can save your game, feed EV berries to your Pokemon until the stat stops decreasing, record the number of EV berries needed to decrease the stat's EVs to 0, and soft-reset the game. If it took less than 11 berries, then your Pokemon's stat has roughly 10 times that number of EVs (specifically between 9 n + 1 and 10 n, where n is the number of berries). If it took 11 berries, then your Pokemon's stat has more than 100 EVs.
source
You can do a similar thing with vitamins, but they will not work if your Pokemon has too many EVs in another stat.