It shouldn't, the OCaml 5 memory model bounds the reach of data races in both space and time. [1] Thread-unsafe code won't be correct when misused, but it will stay memory safe unless you reach for an additional escape hatch (or you find an implementation bug of course).
[1]: https://ocaml.org/manual/5.4/memorymodel.html
I'm much more concerned about the amount of poorly vetted escape hatches in wide use in OCaml, mainly for bindings.