In case anyone is still daring to try to do vision on the Rio, and wants to put it right in their normal C++ project, I was able to (finally) get opencv to build for ARM and integrate into a WPILib project. Been unable to test on a Rio so far, but at least it builds. Here's an
example project with the special opencv build and a file (BuildOpenCV.txt) explaining how to set it up. Was a big PIA for me, so thought i'd leave notes on the steps I went through. You can just throw in your own source files into the project, but make sure to delete/comment out the line #define REAL in WPILib.h, as it creates some conflict of OPENCV. Okay it's 3 a.m I should go to sleep now.