Deckset generates your presentation from a Markdown file. When you write your notes with Ulysses, you can of course use Quick Export to output them as a Markdown file. The more comfortable way, however, is to use Ulysses to edit an existing Markdown file, and point Deckset to it. That way, you can live preview your presentation. Proceed as follows:
I actually purchased Deckset a couple years ago because I was so impressed by its capabilities to turn a simple markdown file into a sharp looking presentation. Using it in conjunction with Ulysses just makes sense.