How often do you want to run a workflow only if the record is created through an import? If the answer is “at least once”, read on.
The only problem is figuring out how to trigger the workflow. Fortunately the solution is dead simple.
Every time you run an import job it generates a unique sequence number of the migration job. That number, appropriately called Import Sequence Number, is in turn stored in each record that particular data import creates and exposed to the CRM GUI.
That means that you can create workflows that trigger on create event and check if the record has an Import Sequence Number to determine if it was created by a data import.
If nothing else, you can use this to circumvent the one record owner per import rule.