I would concur with Jeff on this one.
On the other hand they would be no differant than a regular thru hull except that there would be water running through them no matter what the boats status is, that is being out in the weather. And when rubber gets cold it gets harder and can break.
Personally, I would re-design them so if they were below the waterline, and and if the hose failed they would not take on water.
By glassing or plumbing in a stack, the hose connection is above the waterline. This way if there is a hose failure it''ll still hold water. But still allowing it to drain, in the water or not. Kind of like your rudder support/bearing. If they''re plumbed in (thruhull fittings), they will still have to be maintenanced just like any other thruhll.
You wouldn''t need the seacocks either. It would take a catastrophe event to make them leak. Then you''ll have more to worry about then just your scupper drains..........._/)