ZSS loses to Snake on some stages and wins on others. I think the match-up is pretty even, and is probably a slight loss for ZSS on average, but it isn't a "bad match-up" and Snake players shouldn't go into the match believing they have a significantly large advantage; they don't. The better player is probably going to win. I feel similarly about MK, although I can see why some people think it's dead even; on paper, it is a convincing argument. At the very least, Tornado sucks vs. ZSS and MK can't air-camp or plank her. She also wins in the air as has been said numerous (too many) times.
I think what pushes the match-up to Snake's favor is the fact that ZSS missing a grab means Snake gets a free fsmash if ZSS' positioning is bad, lol.