If you properly disclose what is happening - that's fine, i guess. Personally - if i was aware of a game using a miner, i would just skip it entirely. If you don't disclose it super clearly - it's malware, pure and simple.
Here are some of the things you may want to do when your headset is not on:
- use computer
- watch a video
- use a browser (yes, those things use GPU, shocker, right?)
- look at your screen (who would have thunk it that GPU is used to generate and send images to your screen?)
Also, in the place where I live electricity is not free. I live in a fairly small apartment in mild climate, so when my GPU gets hot - it affects the temperature in the room significantly, it's part of the reason why I have a powerful GPU - to make sure it stays at fairly low load most of the time.
I'm sorry for my attitude, I don't really mean to judge your choices, but calling that miner "genius" is, in my opinion, a premature conclusion at best.