I had another laptop with a hardware switch and a corresponding LED, and it worked exactly as it should - the hardware was completely inaccessible under Linux. So yes, it can be done and it's not rocket science.
Yes, what you describe is trivial - and it would be similarly trivial to design a module that appears to respect the switch (regardless of Linux/Windows) and yet records things surreptitiously, only to offload it at a later date.
Remember the amount of effort VW was willing to expand to cheat emissions testing.
Remember the amount of effort VW was willing to expand to cheat emissions testing.