Question about opencl

You should be fine. However, if you need to check which versions of OpenCL and OpenGL you have, go to the Apple Menu > About This Mac. In the dialog presented, click on System Report... then in the dialog presented, in the left column, find Software > Frameworks and select it. In the list on the right side, scroll down to find OpenCL (and OpenGL) and select those. In the pane at the bottom will appear the details of your currently installed versions.

Example:

(command-click select multiple items)

My understanding is: if OpenCL is present, your mac will use it. And I think if you don't have it, FCPX will not run - it's required: Graphics card compatibility for Final Cut Pro X, Motion 5, and Compressor 4 - Apple Support

FCPX won't use both simultaneously. It will use the nVidia card.