Iapetus is the only major moon of Saturn whose orbit is *not* essentially in the ring plane; it's got a significant inclination. But it's entirely possible that that was not always true.

The rings of Saturn are very, very thin. The tiny moon Atlas, which orbits in the outer part of the ring system, has an equatorial bulge that may well be from accumulated ring material--it looks a little like an elongated flying saucer.