as for API information, have a look here http://pubsvn.ez.no/. Also have a look at ezpedia, e.g. http://ezpedia.org/wiki/en/ez/developers.
Creating a module that accepts http requests to create objects and provides admin/user interfaces to consume these objects is not very difficult.
And there are other ways to interact with 3rd-party systems as well, e.g. SOAP (http://ez.no/ezpublish/documentation/development/libraries/ez_soap/consuming_web_services_with_ez_soap_client).
