I normally don't put a lot of wrist exercises on workouts. I don't think that wrists are the limiting factor to most pitchers. You should work from the ground up. As far as importance goes, your legs should be first, then your core, then you upper body, then your arms. Your forearms and hands will get stronger by simply having to hold the weights you are using.
I guess I won't say that it won't help at all but it certainly shouldn't be the focus of your program.