Hey guys I have seen tons of posts asking on how to get OpenCV to work with Windows and I am here to tell you that it has been solved. I myself did not come up with this solution but, I merely found it and thought I should share it.
Basically, all you need to do is open up Visual Studios, create a new project and go to Visual C++ -> Windows Universal -> DLL and create the project. (You might have to install as it is not default with VS)
Once you have created the project, go to the top Project -> Manage NuGet Packages and browse for OpenCV-HoloLens by Sylvain Prevost and Install it. Once you have this installed you can create a C++ file inside the project for your customized methods for communicating to Unity.
For a better explained tutorial on interacting with OpenCv and Unity you can look at this guys tutorial here
Next you build your DLL and inside your Unity project create a folder called PlugIns and add all of your Dll files from your build to your project and viola OpenCV for HoloLens.
You cannot run your project in the editor as Unity does not support UWP plugins