It's a bit jarring to see a typical Protestant soul effigy above Hebrew text:
Rebecca Polock (1764)
Other gravestones in this cemetery do not have full epitaphs in Hebrew, but give the dates of death using months and years from the Jewish calendar:
Isaac Lopez (1762/5523)
Martha Moravia (1787/5547)
So what's going on here? I'm willing to believe that by the 1760s, the soul effigy had become somewhat divorced from its roots in Christian eschatology and become a formulaic style that said little beyond "respectable gravestone." At the same time, normalizing Protestant iconography is not a totally apolitical venture. I don't know for sure what's going on in that New Bern picture, but I would imagine it might be similar to these eighteenth-century gravestones.
One thing's for sure — I won't assume that slaves who have soul effigies on their gravestones were necessarily Christians.