Yes it needs an RSS feed. Otherwise it's just an mp3 file.
Edit: do you know any podcasts that use an atom feed? None of the 80 feeds in my podcast app are atom feeds.
I don't know any atom feed podcasts (and can't find any), but I can find references to people using (or trying to use) atom for podcasts.
So you are saying you could do HTML without TCP/IP? Would that work you think?