I realized that both Megas gave proper device signatures and responses to the arduino uno acting as their programmer when using Gammon's code. This led me to believe that it could be a usb-to-arduino connection problem and so I looked into resetting the atmega16u2 chip on both boards. I uploaded the usb serial hex file within the arduino firmware directory to Mega #2 without a hitch, but it still has exactly the same problem with exactly the same behavior. Interestingly enough, Mega #1 simply won't go into DFU mode.