Yes, you can add any number of sources to each of your pipelines. Remember, pipelines allow you to use LeadSimple to track and follow-up with multiple types of leads (Owners, Tenants, Buyers, Sellers, etc.) You can then set up multiple sources inside each pipeline to label the leads with in that pipeline.
They can be auto-imported or non auto-imported sources, and they can be different for each pipeline.
Learn more about how to add sources and set up auto-import here.