Good question dawgduck. JC redshirts happen, but not too often and for just the reason you alluded to with your second question. JC's curriculums are designed around two year degrees, so what could one take after two years worth of classwork that might transfer? There are other reasons to do it. You can transfer with a 2 year degree and 3 years of college eligibility left, or you can be drafted at the end of each season from a JC. All these approaches are somewhat risky IMO. Not sure if it's a good option for your son at this point. If he has to redshirt, I would lean towards going to a 4-year school that presents a good fit. Better academics, training facilities, and aftercare. JC baseball can be very very good, but if his goal is to play D1 he'd be rehabbing with better supervision and in a good position to closely observe that level of play. JMHO
In your son's case, a frosh redshirt would mean two straight years out of baseball. Let's all hope that doesn't need to be. I believe you said you'll find out tomorrow for sure. Best of luck and keep us posted.