Why do you think you can't mimic the training benefits of kettlebells using medicine balls, weights and plyometric training that would be more pitcher specific ... and ultimately more beneficial to your pitching? What can kettlebells do that the above mentioned exercises cannot?
I think kettlebells are great. And they certainly have their place in developing explosive, Olympic-lifting-type strength. But for baseball, I'm just not convinced that you would get more from your workouts using them over med balls, weights and plyos. They're just sort of hyped up at the moment, but that hype is coming from a bodybuilding standpoint -- you know, like looking good for the beach -- not a baseball conditioning standpoint, where you're trying to run faster, throw harder and hit the ball farther.