Yes, you can.
Just import the RSS feed of your podcast using the RSS feed importer and keep it in sync with the source.
Please note that the episodes will be copied to Spreaker's servers in order to make streaming possible. This means that:
Only one download-count will appear on your original hosting provider (where your files are coming from), while all subsequent plays on Spreaker will be counted in Spreaker's own stats.
If the files are not in the format used by Spreaker, the audio files will be transcoded.
If at any point your storage quota fills up during the import (or, later on, during syncing) the sync process will be disabled. It will be your task to delete some old content and re-start the file sync.