I actually saw my math teacher at Keystone a few weeks back. He had a baseball helmet on, and he told me that he had just been in a collision where he had gotten hit and fell backward, hitting his head pretty hard. I don't know if he was concussed or not but you should by a ski helmet. From what I can tell, different helmets protect against different types of impacts. Any helmet is better than no helmet but I'm pretty sure a baseball helmet is made to protect a batter from being hit from wild pitches, not catching an edge while blasting a groomer. Look for a helmet with the MIPS system as well, all though it usually has a higher price point. Plus ski helmets add extra insulation to keep you warm.
A good helmet is Like a lawyer, you hope you'll never need it but you'll be glad you have one when you do.