As long as you have defined the custom doc type prior to the import, you should be able to use the Kentico Import Toolkit to do your import. With that tool you can do everything needed for what is needed for Kentico to "recognize" the new records. If you plan to manually import them (via sql script or custom program) I'd suggest NOT to because you'd need to know the other relationships that are needed. You won't simply insert into one table, you'd need to insert into multiple and make references to other records from other tables as you would with any other relational database.
If you're not able to use the Import Toolkit, I'd suggest writing a program and using the Kentico API.