Well, when I think of a swamp ash body on a bass, I think of something like a Jazz or Stingray with a midrange growl and not as much in the way of deep bass response. An ebony stringer in the neck boosts that deep bass fundamental. I guess I wouldn't think of that as a tonal wood combination to try. Would they add to make something sweet or cancel each other out?
I suspect that the natural tone of the swamp ash is suppressed both by being built into a neck-through instrument and by adding the ebony neck stringer. I'm sure it's a great playing and sounding instrument, but I wouldn't count on it sounding like swamp ash. It might, but I'd have to hear it to believe it. If I wanted to hear the ash, I'd probably go with an all maple neck, or maybe mix in a small amount of vermillion or mahogany.
By the way, I have a Zon Sonus with a swamp ash body and love the tone. It sounds very much like a '71 Jazz with maple board that I once owned.