Personally, we don't use those splits that you had mentioned, back/bis, chest/tri's. Typically those splits are used for hypertrophy, or muscle enlargement. Our splits in pro baseball are typically movement based, training the body as a whole, where we teach muscle to fire in sequential patterns, meaning, if we are training a leg movement, it would typically result in upper body rotation, which is exactly what happens with hitting, pitching, etc.
The classic body builder splits you mention are slimmly relevant to our sport. Increasing arm strength has minimal carryover to baseball in terms of performance gains, since performance is usually enhanced by efficient movement of the whole body. This is where the core comes into play, being a bridge between the upper and lower body, if strengthened properly it will lead to better force transfer between the lower and upper body, which will allow for greater rotation.
I think you need to re-define the "why" behind your goals. Why do you want stronger arms? or a bigger chest? etc? Then the program design process will begin for you.
Dana Cavalea
New York Yankees
www.mlstrength.com