I just wrote a reply to this, and somehow it looks like it did not post, so here goes again. To answer your question, correct, Induction's built-in DI system cannot be used from outside of Induction. However that said, you should not have an issue accessing your EJB based services from a batch context. Remember your services themselves have no dependency on Induction.
So basically you can instantiate an instance of your service EJBs the same way you do it in your Induction factory for the respective service. In fact, you may even choose to call the createModel(...) method of your factory class with the appropriate parameters to create an instance of your service.
Hope this helps.