You don't NEED a bilge pump but a good sub can fill the engine compartment with water and it would take a lot of straight wide open throttle riding to suck it out. They're cheap and it's the off season so go ahead and install one.
My bilge switch broke a couple years ago and I just use an alligator clip before I start riding, close the hood, then open the hood and unclip when I'm done. It's ghetto but while your ski is running you won't run down the battery. If you forget and leave it on you will. My bilge has been running like this for a few years with no problems. I've also just zip tied a bilge pump in place. I'm thinking about all these short cuts because if I were you I wouldn't put to much time/money into a JS I'd be looking for a square nose.