It's not like the snakes are just hiding out waiting to bite you. JFC, if you hit your ball out of bounds, just follow the rules of golf and use a new ball. The snakes aren't going to bite you unless you walk right into them, and it's not like they are going to catch you unawares if you are playing within the area that you are actually supposed to be.
The course absolutely should put up signs warning golfers to watch out for rattlesnakes, though.