On older post https://forums.oculus.com/developer/discussion/41074/osp-unity-wwise-integration mentions looking for AkSoundEngineStubs.cpp. But I can't even find that file. I double checked my Wwise 2017 install to make sure I have the SDK installed and it says I do. This step isn't that clear to me in the documentation.
I don't think this step is specific to any version of OSP but I'm using 1.17.
Ah ok, I went through the steps but I copied the oculus spatializer dll for the 32 bit version over and not the 64bit version. I had the 64bit version installed in wwise so there was a mismatch. That fixed the unregistered plugin error I was seeing.