In Maine there is likely overlap between just about all varieties. Compatibility with apples is only about blooming with at least some overlap where enough flowers of both are open at the same time and whether a variety is a triploid, making it useless for pollination. The further south they are grown the wider the spread time between early and late blooming apple varieties.

I don't think either variety is triploid, but that's probably all you need to search for.
What may be frustrating is that Zestar will likely begin flowering a couple years before Sw 16, being a far more precocious variety.