You don't need to circulate the water in a rice cooker. You do get more variation in temperature than you would get with a real circulator, but it's not enough to matter unless you're doing fussy egg cooking. For most cooking, a noncirculated rice cooker water bath worked just great for me.

Convection vs. circulation. The heat comes from the bottom with rice cookers and crockpots.

Aquarium pumps work quite well, but it is not strictly necessary.

I'm going to have to try this because why not?