Yes users sometimes post audio of their Sonic Pi pieces. Usually this is done by uploading them to a site like soundcloud.com and putting a link to it in your in-thread post. You can get a free soundcloud account for storing up to 1 hour of music.
As regards transcribing music I have done a fair bit of this, starting with a midi file in MuseScore and then using a script to convert each part separately to a Sonic Pi file, see this I have also written a project to allow Sonic Pi to play midi files directly. see here