Hello James,
Using Hauptwerk to create MIDI or audio files for public download from the Internet (Contrabombarde or elsewhere) definitely doesn't make your Hauptwerk installation a public one, and thus doesn't need a public installation licence.
However, the Free Edition isn't allowed to be used for public performances (including publishing to the Internet).
We did actually send you an email offering you a free Hauptwerk v4 licence upgrade before Christmas during the beta testing period in support of your work (although perhaps you didn't see that due to your time in hospital), so there's no need for you to be using the Free Edition. If you didn't already take us up on that offer, please just send us a licence update request file and we'll enable v4 for you now. Thanks.