As this was the first post I found when searching for "nsight optirun" I just wanted to wanted to write down the steps I took to make it working for me.
Go to Run -> Debug Configurations -> Debugger
Find the textbox for CUDA GDB executable (in my case it was set to "${cuda_bin}/cuda-gdb")
Prepend "optirun --no-xorg", in my case it was then "optirun --no-xorg ${cuda_bin}/cuda-gdb"
The "--no-xorg" option might not be required or even counterproductive if you have an OpenGL window as it prevents any of that to appear. For my scientific code however it is required as it prevents me from running into kernel timeouts.
Happy bug hunting.