I think Allen, Rahn, and Sickie have brought up some good points worth considering.
Noise - Hard to tell how loud it is from the video, but the motor noise might detract somewhat from the effect depending on what other ambient sound you have.
Grain in the eye/hair - The hair part is really not that much of an issue unless someone is like Sickie)) and finds it annoying. You do want to consider the speed at which the rice grains are being thrown and whether they might pose a risk, however small, in terms of hitting someone in the eye. The tendency will be for people to look up when they feel something hitting them from above.
Another safety point to consider - How slippery does the floor get once you have a lot of rice grains on it?
I think the idea is a good one, just think through some of the potential issues.