Does this marketing actually work? If so, then I could charge people $5000 for a 'job skills development course' with a money-back guarantee. Maybe I make them read a book or something so they don't get suspicious. If they get a job, I profit; if they don't, no real loss to me. If 30% of the people find a job, then my expected value is 0.30 * $5000 = $1500. Plus even if someone doesn't find a job, they might not bother with the hassle of turning in the guarantee(the old rebate trick). The guarantee is free money for me even if it's completely ineffective or even actively harmful to the person.
Udacity are mainly online courses, so I imagine it's pretty low-cost to offer their courses to people who turn in the degree. It seems like one should be suspicious of altering their trust level in Udacity even with this guarantee.
Then again, it does at least get the incentives right for them, since they would make more money with a better program. So in the long-term, maybe it's a good thing.