What, you mean the sound Eevee makes? I think it's close enough, and I don't expect perfect pronunciation from Pokémon anyways. Some of 'em can't even say their own name. Krabby comes to mind.
For those interested: the difference in pronunciation stems from the fact that the Japanese language doesn't have a "V". For that reason, the Japanese don't know how to pronounce it either; There's no reason to learn. Eevee's name in Japanese is イーブイ or iibui. That "bu" part has to stand in for the "V", and that's pretty much the best they can do to come close to saying Eevee.