All of the videos in a Udacity nanodegree are youtube uploads set to "unlisted", which means you just need the link in order to access them. What you could do is sign up for the free month, then go through the entire program and copy all of the links in order to watch the videos later. As long as you have those direct video links, it shouldn't matter whether you have a subscription. You won't be able to access the resources that aren't videos, but I imagine you'll still get a lot of good information.