Markdown is subtle and tricky? No, in fact, it isn't.
I’ve had a really good subsequent exchange with Ulysses customer service and, mea culpa, I misunderstood what they meant, due in turn to their misunderstanding one of the questions I had asked. They do, in fact, see Ulysses as an editor with Markdown underpinnings; and when one uses Ulysses to edit an external .md document, Ulysses indeed behaves like a straight-up markdown editor. (I’ll have more to report after this weekend, during which I’m trialling Ulysses again…)