I think I would challenge whether adding a necessary entity (to satisfy the FK requirement) needs to be in the same transaction as the overall dataset processing.
If an Employee, for instance, can be added by any of several ETL processes, does it really matter if one is added outside the main transaction of the ETL dataset? If not, then make the adding of a required entity happen in a separate transaction and commit that transaction before continuing with the main ETL process. That way the ETL process can continue and other concurrent ETL processes can also see that new entity when they get to the point of needing it. If one of the ETL processes ended up failing at some point perhaps a few new entities were created and not removed during the rollback of the ETL process but is that really such a problem?
