Hi NicoX,
I don't know the answer to this one and I can see that there could be an issue, from looking at the info on the Noctua website, but I have not had any experience of this myself.
That said, I would probably be prepared to try fitting the cooler and if I encountered a problem with the proximity of the Cooler to the backplate of the GPU then I would do a little modding to overcome the problem. All you need to do is make sure no metal part of the cooler is touching the backplate on the GPU and a thin sheet of plastic or some strategically placed rubber grommets should suffice to achieve this.