You can perform a find or constrain the found set specifying criteria that only finds those records, such as putting a lone = sign into a field to find records where that field is empty.
Then Delete All Records (which really only deletes all records in your found set) can delete them.
You may find this thread of scripted find examples to be helpful: Scripted Find Examples
Yes, you can confirm it doing on another file for testing. You should check the found set (perform find has succeeded) before delete all.
For your purpose, you may be able to set some fields validation "always" "not null", then when imported the records will be removed automatically.
I wonder 1 year old question is now alive.