I have no experience with this but in my mind, it should work. The problem I see happening is if the ski is turned off and for some reason has water getting in the hull the pump will push water into the water jacket.
I am not sure how this would work while the ski is operating. It's possible that the bilge pumps harder than the water that's going into the water jacket and could cause it to backflow.
Maybe someone with more experience has a definite answer for you, but I would probably just play it safe and just drill a discharge part.
Afterthought: Maybe you could make this work by getting some sort of high flow check valve that stops the water from back flowing into the motor. I use
one of these on my fish tank to keep water from flowing out in case of a power failure. It hasn't let me down, but I do have to pull it off and use a bottle brush to clean it out at least once a month. All and all it seems like it could work, but creates a potential failure spot.