I think Yoga is fine for baseball, especially the mental approach, but yoga is far from perfect.
In some cases it actually is bad creating extreme flexibility where one actually needs stability.
For instance, I'm not sure what the position is called, but it is basically a deep back extensions. The spine was made for stability, not flexibility, there are also a few leg positions that take stability from the knee and ankle in favor of flexibility, which I do not like.
To much flexibility where stability is needed will often result in injury or a loss of power.
I really always looked at arm band work as prehab for shoulder longetivity and never anything that would really gain velocity.
Long toss is the only potential velocity boost that I really see from what he did.
No doubt Zumaya has great genetics as well.