How do we check rehires/duplicates when posting Pending Workers via API?

We have a vendor who will be creating Pending Workers in our system through the API workers endpoint. Before they send anyone over, we need them to run a duplicate person or rehire check. They want to do this using the SSN or national identifier.

Is there really no way for them to query the workers endpoint, or any other endpoint, using only the SSN or national identifier?

We’ve talked about creating a custom endpoint in OIC as an alternative. The problem is that we’ve already hit the 15‑address IP whitelist limit in OIC, and we’ve avoided building new endpoints because of the heavy network workarounds required to get traffic in.