Randy's link will give you when you can actually collect DI based on visual obervation or surname, but if you're asking whether to leave it blank or mark No when the information isn't taken face-to-face, that is not yet clear.
For HMDA, where the information is not collected face to face, the visual observation questions should always be N/A OR always be Not Collected based on visual observation (or surname). I spoke with the CFPB in January, and they said it would be clarified in the next rule that was written. I'm in the Not Collected camp because it doesn't say anywhere that it can be N/A.
Just be consistent and ask for a citation if anyone says your wrong.