Jump rope is a great conditioning, agility and foot work tool all baseball players should use.
However, it won't do much for your vertical jump.
There are certain lifts that increase vertical jump very effectively. Some of these include Power Snatch, Squat (all variations), Push Press and Deadlift.
What really increase the VJ (and speed for that matter) is strengthening the posterior chain, especialy low back, glutes and hamstrings. This is where the power comes from.