A CPU and GPU die are both pretty much the same thing, a paste that works on one will work on the other.
However, it is not recommended to use conductive thermal pastes like AS5 when it comes to GPU's. The GPU usually has transistors around it, and in the process of mounting the cooler the thermal paste will most likely get all over them.
So having a conductive paste could cause issues. I used Arctic Cooling MX-4 on my GPU and I havent had any issues so far.