If they can write blog posts, they can podcast. This is the same behavior natively in WordPress as well.
You can turn on roles and capabilities in PowerPress > Tools menu, then you can customize which users can see the podcast episode boxes. If the user is tech savvy and can access the custom fields, then they can still podcast if they have the knowledge how to manually create an enclosure.
As far as uploading media, most servers have file upload size limitations due to limitations to PHP. They will most likely need FTP access. Furthermore, you do not want to host your podcast media files on the same server as your web site, it will cause bandwidth and page loading issues once your podcast starts getting traction.
This is all documented on the Blubrry podcasting manual, http://create.blubrry.com/manual/
