I think submitting the demo might be better - just to show that they have completed something. The whole 'copy and paste in the box' thing in NaNoWriMo, was a way to detect how many words you had instead of saying 'I have x words'. sort of like proof (given you were allowed to scramble in case you were paranoid, it still left room for cheating, but it was more tangible than stating it).
People might not want to submit source code, especially if they wish to use what they've got (or what they may develop it into) for commercial purposes. Even if you weren't to show anything publicly, people who want to enter may not trust the site. (Hence NaNoWriMo lets you scramble, I scrambled mine, because I am one of the paranoid few
)
But I'll be willing to offer any input from my experience in partipating in NaNoWriMo, when and when you need it.
--The hatred of those who harbour such ill feelings as, "He reviled me, assaulted me, vanquished me and robbed me," is never appeased.--