1. If it's against the rules, then you shouldn't have one, but I know everyone tends to break that rule at some point in a dorm.
2. Your roommate has the right to enjoy the room just like you do. If he is afraid of snakes, then respect that fear and see if you can room with someone else. Talk it out with him, and explain you understand. A lot of people fear snakes, and with some talking and you pointing out how secure the cage is, and how tiny and harmless the snake is he might give it a try.
3. Keeping it quiet is a GOOD bit of advice. People do dumb stuff to snakes in general, and to keep him safe, keep him quiet.
Just my .02
Wolfy