First off that sucks man and I hope you have as speedy recovery. I would not recommend it riding with a cast. But if it was my, I wouldn't give a shit if I had a neck brace. If it's winter and I am physically able to ride, I am. I don't care, every single opportunity I have to ride I am going to take, risk to my health be damned. I am not going to let anything stop me. If I die from it, that sucks I would rather die doing what I love than being 90 in a nursing home shitting my pants.
Sorry for the rant. All in all, not recommended, but you gotta figure out whats more important. Your health or snowboarding.