Well it is not even required that you have the initial revision, but that you have the "last" revision. If you are importing data, I think the best solution is to keep everything consistent and for all new inserted rows create a "0" revision. That is:
1. insert a new row to the revision table, write down the id
2. insert the rows into the target table
3. insert corresponding rows into _AUD table using the revision number
I think finding which rows need to be inserted into _AUD tables can be done using SQL as well.