The OpenCV included with JetPack does not have CUDA support. Why this is is because Nvidia is apparently not satisfied with the code quality of OpenCV’s cuda namespace. Not all tests pass on Tegra (or on x86 for that matter).
I am of the opinion that Nvidia should support OpenCV since it’s an industry standard and developers are forced to use it anyway, but I don’t work for Nvidia.
You’ll have to build it from source for cuda support using a script like this: