Quinoa in a Rice Cooker?
Rice cookers are quite versatile and cooking Quinoa would not ruin the rice cooker if you do indeed want to experiment.

A rice cooker works because there is a springloaded thermal sensor plate at the bottom of where the metal pot sits(only if it is automatic. Some rice cookers have a switch to flip to go into the heating process). This will then start the heating process to boil to water. Because boiling water do not rise above 100 degree Celsius, the sensor can tell if there is still water left in the cooker. Once the sensor reads higher than 100 degree Celsius, this means the water has all boiled away. At this point the rice cooker goes into a sitting phase where the steam will continue to cook the rice and the rice is allowed to expand.

With this knowledge, we know that the main problem you would come across when cooking Quinoa in your rice cooker is getting the correct ratio of water to Quinoa grains. If you use the same amount of water you use for cooking rice, the Quinoa might turn out softer than desirable. 

Take a look at this link: http://glutenfreegoddess.blogspot.com/2009/01/how-to-cook-quinoa-super-easy-way.html. It provides some information in regards to cooking Quinoa in a rice cooker. It seems to suggest 2-1 water to Quinoa grain ratio (which is typically what I use for rice too).