MLB Fanhouse points to an article in which Giants outfield Dave Roberts is said to have helped Dodgers pitcher Bret Tomko with his delivery. Fanhouse notes:

The immediate question that must follow is whether or not Dave Roberts crossed a line in tipping his friend, who happens to pitch for a hated rival. Think about it -- do you see the players in the final showdown at the World Series of Poker tell each other their bluffs after they've finished? Of course not -- they know they'll meet at some point in the future and want to keep that privileged information to themselves. So what do you think, is it OK for Roberts to give a tidbit to his buddy, or does that cross the line of competition? I think Giants fans already know the answer.

But if you read the article, it's not at all clear when Roberts and Tomko talked:

Now, Tomko's mother is cancer-free. His wife is healthy. And he has used a new delivery inspired by a discussion over dinner with Giants outfielder Dave Roberts, a fellow San Diego-area resident, about how hitters were seeing the ball all too well against him.

So these two could have sat down for dinner when Roberts was a free agent. In that case, I don't see the problem giving advice to a friend.