Spotfire should be able to open lists and files from SharePoint Online and for example from http://servername/test.xls. If we were able to link the server name as a mapped folder, you can make it work, but otherwise you need to download all the files to a local folder(s) and create the links from these into your DXP.
Our organization was looking to connect to Sharepoint on Office 365. Would this "idea" include that option?