If pro baseball is the kids dream, then as a parent I would support it. He's got resources and talent to show. As a parent, I would do a ton of research and advise my son of the many pros and cons. Having lived across the street from an MLB player, I got a sense of how difficult it is to play professional baseball.....it takes ridiculous skills, commitment and luck. My only concern would be does this (or any) 17 year old truly understand what ridiculous skill, commitment and luck looks like.
My son's dream was very different. He stuck to his plan of 4 years of college baseball then pursue his college major which he was passionate about.