Commercial prepared rice is naturally hygroscopic at most atmospheric relative humidity levels. It does indeed absorb (or loose - dependant on the relative humidity and the moisture content of the rice grain) water through the husk as the hull is not at all a complete water barrier. Rice is typically dried for shipment and storage to reduce water content, and that is done without removing the hull.
As a hygroscopic material it does certainly work as a mild desiccant. There is no "myth" as people have been using rice as a desiccant for centuries. Admittedly it is not a terribly effective desiccant, but it still has those properties.
No, it does not act like a sponge and suck up liquid, no desiccant works like that. But if you put uncooked rice in a high humidity environment (such as a sealed plastic bag with a wet item inside it) the water content of the rice will most certainly increase as it takes up moisture from the air. That in turn will help lower the humidity in the bag, drawing (hopefully) yet more moisture from the wet device. Rice absorbs water in its vapor state, not slurping it up like a sponge. It dries items by maintaining a disequilibrium in humidity, like any desiccant does. By keeping the humidity level below equilibrium, it helps to draw water out of the wet item sharing the same closed environment. If the humidity ever actually reaches equilibrium, then neither the wet item nor the rice will gain or loose any further water content.
<edit> BTW, salt itself is also a desiccant material. The reason rice keeps salt from clumping is again, it help to maintain a dry atmosphere around the salt, so the salt itself does not absorb excess moisture. It is basically acting as an antagonist desiccant to the salt itself. You will never notice any observable change in rice, even though its measurable moisture content may go up (or down) by as much as 15%-20%. Although, if its moisture content gets high enough, it becomes very prone to mold infection and may get darker in color.
