A long time Citrix hasn’t supported the Desktop Viewer for XenApp. Originally the Desktop Viewer is used (and delivered) with XenDesktop. However more and more people have been using the Desktop Viewer also for XenApp. Until now this was not officially supported and if there were any problems likely you’d be redirected back to the supported way.
With the release of Receiver 3.3 the use of Dekstop Viewer in combination with XenApp 6.5 is supported. Here’s a snip from the eDocs of the website:
Hosted Shared desktops. Receiver for Windows now supports server desktops published with Citrix XenApp. The desktops are displayed through the Desktop Viewer. To configure this feature, see the XenApp, StoreFront, or Web Interface documentation.
The use of the Desktop Viewer is only supported with Receiver 3.3 and is not backwards supported. So if you want to use the Desktop Viewer upgrade to Receiver 3.3 before making the support call. Besides the support for Desktop Viewer version 3.3 has also some security fixes.