unreal engine 5 integration plugin causing VR Hands rotation/tracking to be incorrect

We discovered the same problem also.
For some reason (post your favourite meta conspiracy theories below), when you go for the XR API: 'Oculus OVR Plugin + Open XR' the hands are rotated as you describe, compared to 'Epic Native OpenXR with Oculus vendor extensions)
There have been many people 'attacking' meta over various issues with the plugin, relating to OpenXR, which I wont revisit here; a web search will surely fill you in if you missed it.

This has been just one in a fairly long line of 'pain points' for us with Quest development, the resolutions of which have burned a shocking amount of dev time. As a result we made the decisions to:
- Use the Epic Native/OpenXR and completely ignore anything potentially proprietary from Meta

- Stop using Meta's fork of the Unreal Engine, and only use Epic releases.

I have to say, this has made certain things feel a little more stable, and allowed us to continue cross platform development of plugins which are NOT tied specifically to Meta/Quest headsets (as we need PCVR support too).
Of course your specific needs may vary, and you might require additional features which only meta's fork, or the Oculus+OVRPlugin provide. 
If that's the case, you are probably specifically targeting only HorizonOS, and are safe enough rotating your hands to the positions which are correct for that platform (currently!)