Yes
(Kind of)
EV reducing berries were introduced in Pokémon Emerald, and when used in Ruby and Sapphire They have no effect. However, there is a roundabout way of reducing your Pokémon's EVs. If you trade your Pokémon to Emerald, you can use all the EV berries you want, and then trade them back to your Ruby or Sapphire game.
This is technically not in Ruby and Sapphire, and if you have Emerald there's not much reason to play Ruby and Sapphire in the first place, but it's really the only way if you are set on fixing your EVs. Just find a fried who has Emerald is is willing to use their berries on your Pokémon.
If you want to find a way that is only in Ruby and Sapphire, cheating is the only way.
Source: My experience with Gen 3 games.
Hope I helped.
