It is in our plans to extend the collection of existing data sources and provide you with means to directly use XML, CSV, Excel files as data source for your reports. Meanwhile, you will have to read the XML into a DataSet or other custom business object in order to use it in a report. Then you can utilize the assembly that reads the XML as elaborated in the How to use external assemblies with custom CLR objects in the Report Designer KB article.
New HTML5/JS REPORT VIEWER with MOBILE AND TOUCH SUPPORT available in Telerik Reporting Q3 2013! Get the new Reporting version from your account or download a trial.