Do I need to install CUDA and Nvidia Web Driver to use OpenCL on Nvidia GPU?
No, you do not. OpenCL and Metal will run automatically on the Nvidia GPU. If you want to take advantage of Nvidia's CUDA architecture (which I highly recommend for software that takes advantage of it, like the Adobe CC suite), you need to install the CUDA driver. You do not need to install the Nvidia web driver because your machine has a built-in Nvidia card (the driver is built-in to MacOS).