Could Hadoop be used as a mining pool architecture?
Map Reduce isn't the best idea, because distributed mining is solved and works well.  The magic of mining is described here, and when that is complete that Bitcoin protocol allows for 25 new Bitcoins to be send to any address.  This is encapsulated into a block that is either accepted (and used as the "previous" block), or rejected, for example if the protocol rules are broken.

Your time is best spent running your own mining pool.