A passport number is acceptable for CIP:
(4) Identification number, which shall be:
(i) For a U.S. person, a taxpayer identification number; or
(ii) For a non-U.S. person, one or more of the following: a taxpayer identification number; passport number and country of issuance; alien identification card number; or number and country of issuance of any other government-issued document evidencing nationality or residence and bearing a photograph or similar safeguard.
There is no uniform way to validate a passport number beyond physically comparing it to the passport. You are not required to verify all four pieces of information you obtain.
The IRS considers payments made based on the time value of deposits as interest, not dividends. Payments of interest and dividends to NRAs are treated differently.
If an account is interest bearing, you will require a W8-BEN from each NRA owner regardless of whether they have an SSN. If you do not get one for each NRA owner, then you impose backup withholding. You do not get the form and also impose backup withholding.