The WPF ReportViewer uses RadControls for WPF in its template, still Telerik Reporting does not require you to purchase both products. The viewer of a specific major Q release is built against the corresponding release of the WPF assemblies, and we ship trial version of these WPF assemblies, which are internally unlocked when used with the viewer.
In cases you use both products, the above approach allows you to upgrade them separately in the frame of a Q release by adding the binding redirects to the configuration. Then on upgrade you will need to run both Upgrade Wizards and manually edit the configuration file with the bindings.
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.