There are multiple parts to the picture.
Platform Support - Support for passing a GPU though to a VM
VM - Remoting support - Integration with a remoting protocol to efficiently access the frame buffer of the GPU, encode the content and send it to a remote end point.
Neither part of vDGA is supported today with View or XenDesktop.
I did not realize we had released the whitepaper with the steps for enabling the tech preview of vDGA. If you follow that guide you can get things going. From your message above it looks like you are missing a key step from page 19.
Note - You will likely have issues with the K1 / K2 as the bit in the preview are not updated to properly support K1 / K2.
WP