vulpina, sort of, but their not really 'air stones', they're called 'bubble curtains', at least the brand I got are called that...ooh, here's a URL w/ a picture/description on it:
http://www.homeharvest.com/hydrosup.htm, they call it "Air Bubble Cascade" there. Anyhow, no, the roots don't need to dangle in the water, they can be out of the water -- the idea is that the bubble make the air so humid that the plants grow on that...plants that stay in aero for a long time tend to have their roots in the water, and it doesn't seem to hurt them, but I almost always take mine out way before the roots are in the water...