I had Pre-populate all the users in a specific OU for RODC. Exporting the objects from ADUC exports their CN name and not the SamAccountName.
This powershell script would help extract the output to SamAccountName format.
Get-ADUser -Filter * -SearchBase "OU=Users,OU=COL - Columbia,OU=States,DC=DomainName,DC=com"| FT SamAccountName -A >a.txt