Maybe they could, but it's not a good idea.
Pokemon are stronger than humans, so there'd be no reason for them to use humans for anything.
Also, Pokemon grow faster from experience with humans, as shown by the fact that they get more Exp. from trainer battles than wild battles and get boosted Exp. when they're traded. The more humans that are involved, the faster the Pokemon grows. In addition, every wild Pokemon, regardless of what level it's caught, doesn't have any effort values, which implies that those come from being with humans, too.
And that's not even getting into the technology that humans have. Why fight for your life in the wild when you can have delicious poffins/pokepuffs/curry, a warm safe Pokeball to live in, and if you get hurt or even tired, you just need to be placed in a tray and you'll be okay in just a couple of seconds.