Hi Joe,
When you upload a File Geodatabase or Shapefile, the zipped file is uploaded and will be listed as the correct Type. Users in your organization can access this File Geodatabase/Shapefile (if you've shared it) and download it to their desktop. This is just another great benefit of ArcGIS.com.
A Feature Layer is created when you check the option 'Publish this file as a feature layer' when you are uploading the zipped file.
To answer your question, no, this file is not needed for the Feature Layer.