Can a user use a US Tax ID or TIN instead of a SSN for KYC checks?

Yes, you would be able to input a TIN in the SSN field...

Yes, you would be able to input a TIN in the SSN field and if the investor is listed in any of these databases that our KYC check is run off of, then the investor could get an approved response from the KYC check. Here is the list of databases we check against:  KYC/AML Information