Answer: In a brief search I was finally able to locate a listing of plants indicating salt tolerance and including a related Styrax, S. grandifolia. (This list was from Florida where they are very aware of salt tolerances in plants.) It indicates that Styrax has no salt tolerance. I would expect that to hold true for the related S. japonicus, especially since yours is a woodland tree that absolutely requires evenly moist (yet well drained, meaning damp but not soggy) soil. Salt interferes with the roots ability to take up water.
In my experience with S. japonicus it is a typical understory tree and needs a woodland type of soil that is acidic and humusy, a spot with morning-only sun or very bright dappled light all day, and shelter from winter winds. So all in all I do not think it would be a good choice for you. Your local professional nursery staff may have some suggestions based on a more detailed understanding of the growing conditions and your design goals for the site. I'm sorry I can't be more encouraging, it is a lovely tree in the right situation.
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