MLB Rule 8.02 A pitcher shall not:
(4) apply a foreign substance of any kind to the ball.
So, the initial thought is a technical "no."
Do pitchers at every level, including the MLB put stuff on the ball? You bet. They take the chance that they won't get caught.
I personally saw a AAA game a year ago. Sitting next to the bullpen. One of the relievers pulls out a chewing tobacco can and begins to rub the substance inside it all over his non-throwing arm's wrist. Asked him what's in it. He kindly gave me and my buddies (who are pitchers, I am not) the recipe.
I've heard stories of Greg Maddox putting icy hot on his back. When he would sweat, it would mix with sweat and create a slippery substance. Said substance would roll down to the seat of his pants, which is why he was constantly picking his seat. Is this true? I'm not sure. Is it funny? You betcha.