>Do I understand correctly that if my VFP date field is empty the upsize wizard will convert the record and will make the datetime field (in SQL Server) as NULL? And if my VFP date field is outside of the range of allowed, the upsize wizard will treat this record as an error?

No, If you want your application to work with VFP tables and SQL Server, it's better to convert empty dates to NULLs in VFP too.