I am currently enrolled in that program. The program is great (I still don't believe it is so cheap). But it is not because of Udacity. It is great thanks to Piazza, professors, TAs, remote office hours, projects, students, Canvas, Slack groups, OMSCS subreddit, GaTech HPC clusters, remote labs, software licenses, student perks, and various other internal GaTech services. Udacity is just a small tool there to present a list of videos. Not a lot of professors use it for anything else. Hell, on Piazza for most courses you can even find a YouTube playlist because the Udacity web and mobile apps are incredibly bad compared to plain YouTube.