Does anyone know if there is any way to convert JSON feeds - from public web services - into apex collections?
AFAIK there is no built-in functionality to consume JSON in Oracle as well as APEX. For processing JSON in PL/SQL you have PL/JSON , if you want to go that route.
My personal preference is jQuery.parseJSON . You can use this in conjunction with AJAX/ On Demand process to load the data into APEX_COLLECTION.