Hi Rob,
The upload URL should be a program which accepts the file stream and returns acknowledgement. Look like the above mentioned URL is a shared file folder. UI5 cannot directly upload document to a folder until unless if you have a program e.g., a servlet which reads file and you should mention the servlet url in FileUploader control. If you are working on Java stack then you can use any open source file upload servlets using Jersy.
As mentioned in the document "Response message which comes from the server. On the server side this response has to be put within the "body" tags of the response document of the iFrame. It can consist of a return code and an optional message. This does not work in cross-domain scenarios.", it is the responsibility of server side program to return the response tags.
Thanks
Abhilash