Reckon it would be worth a try. I bet the water flow over a normal prop blade is diagonally outwards due the the centrifugal force of the entrapped water and there will be drag formed at the tip of the blades where the waters from the front and back of the blades meet at different speeds. I would also put money on there being a tendency for the water on the high pressure (forward) side of the blade to attempt to leak over to the low pressure side, particularly at the tip. If the ring is able to exert some control over the this, it might be a good thing.
Of course, pehaps that's all Cod's wallop.
Apologies, Cod. The urge just overwhelmed me.