The built-in "music.listen" action is indeed very restricted, from https://developers.facebook.com/docs/technical-guides/opengraph/built-in-actions/#listen:
In order to access the built-in Listen action, you must have the
appropriate relationships in place with rights owners. We are slowly
increasing the number of developers that can leverage the built-in
Listen action. If you are interested, please complete this form and
e-mail it to musicdevelopers@fb.com.
That means, Facebook is enabling music.listens only for the right-owners of the content. For a podcast-app I think it will be very difficult to proove this rights.
What you could do: use a custom-action "play" or similar. When using a custom aciton, please keep in mind that you're not allowed to publish this action passively / automatically starting February 15th, 2013! You can only publish these actions, when a user chooses to do so explicitly (which means, an app that publishes all played podcasts automatically is probably a not possible).
What you should not do at all: use a custom action "listen" - this will surely NOT get approved.