The sample programs from the old RealSense Unity Toolkit, such as the object tracking one you quoted, will unfortunately not work in SDK 2.0, as that new SDK and the old SDKs have completely different architectures that have no compatibility with each other.
To use those programs, your customer would need to use an older RealSense SDK program called '2016 R2'. If they have not got it already, a 1.8 GB direct download link for it can be launched in the browser with the link below:
If your customer wishes to use the latest SDK 2.0 with the latest camera models such as RealSense D415 or D435 then Unity is supported in that too and it should work with Unity 2017 and 2018. It currently has limited functionality though compared to the older SDK's Unity support (it can stream a texture into Unity or generate a point-cloud type depth scan). D415 and D435 will not work with the previous SDKs, so using them with those older sample programs is not an option.
Unity support in SDK 2.0 is provided via a Unity 'wrapper'.
Since SDK 2.0 Unity does not have built-in gesture support, the best way your customer may be able to do it is to integrate the OpenCV camera software into their application. There is a pre-made system for doing so that can be purchased in Unity's online Asset Store.
RealSense SDK 2.0 fully supports OpenCV outside of Unity. I would speculate (though do not have certain knowledge) that the SDK's functions may be able to be accessed in Unity through C# code, since Unity for SDK 2.0 works through the SDK's C# wrapper. I do not know the programming protocols for doing so though.