First, are you asking whether you can record through the dock connector on the bottom of the iPod, or are you asking whether you can use a specific remote control accessory to record?
It is possible to record using the dock connector if you buy or make a connector with the appropriate pins (I believe that there is information on the ipodlinux site about the pinout of the dock connector).
Second, are you asking whether you can use headphones as a microphone for the purpose of recording? If so, the answer is yes, although headphones tend to be quite inefficient when used for this purpose. If this is not your question, then I'm not sure what you mean by "via earphones."