Large quantities of sushi rice in a rice cooker?
Sushi rice in a rice cooker would be cooked using mostly the same ratio as other rices.  I tend to add just a touch more water than I would if making, say, basmati rice just to make it a bit sticky.  Since the standard rice-cooker formula is:


Rinse rice a couple times and mostly drain
Add equal quantities water as rice (e.g. 2 cups water for 2 cups rice)


... for sushi rice, I add just about 10% more water, e.g. 2 1/4 cups water to 2 cups rice.  This makes it just a touch stickier.  Optionally, you can throw a piece of konbu in the rice cooker for extra flavor in the rice, but I've never found it to make much difference.

Of course, if you're making sushi rice, you'll want to take the rice out of the rice cooker as soon as it's done, spread it in a large pan, and season it with vinegar, salt and sugar and cool.

I've made nori rolls using rice cooker sushi rice several times; it works fine, and most of the sushi you've eaten in restaurants was cooked in the rice cooker.  Making it the old-fashioned way (soaking the rice in cold water etc.) results in somewhat better rice texture, but it's a lot more time.