Dropouts are 6mm steel plate, trust me, the derailleur (correct spelling) will die long before the dropouts do. To fit 12mm axle, depends, you could get it slotted out to suit (which is what I intend on doing), and there's plenty of material to allow that, or you can get axles with 9mm flats machined into them to fit.
Either way, awesome bike, and having a chunky rear hub will suit it quite well.