Question: How can I most easily export a Blender 2.8 scene to a Vive VR device? (I'm not talking about using Blender *while* wearing a headset; I mean just exporting a scene to be handed-off to a different PC with a headset.)

Answer: 
There exists a work in progress plugin thats claims to be able to view blend files in VR: <https://www.youtube.com/watch?v=9qAC8FTrU5s>

The HTC Vive Virtual Reality Headset is basically a Display. It has no software to show things by itself. So equally to your computer screen it can't open Files. 

First option would bee to find some software that is able to display 3D objects on your VR-Headset. You can import .obj/.mtl files to tiltrbush with some fiddling - maybe something more general exists. And after that you need to figure out the details how to export to that specific software.

Option two would be to create software that can render to your VR-Headset. That is easiest done with a Game engine like godotengine (open source), Unity3d or Unreal (proprietary with free entry level licenses).
I Would personally recommend Unity3d as it is beginner friendly and has nice Blender integration.
Making things look god in a game engine is some one topic of study though.
I suspect this may do what I want:

<https://store.steampowered.com/app/891420/VR_Model_Viewer/>