Very plausible. A Google settings backup from a prior device, that had more notification settings, being imported into the M8 and causing havoc with the LED settings. Moving from Samsung settings -> HTC settings could be problematic.
Or a prior application that worked on a prior device, being imported into the M8 and causing havoc with the LED.
So skip the initial set up step where you import settings (and applications) from Google, and magically the notification LED will work fine.
I outlined a safe mode and diagnostics test, but it is largely ignored as well.
(the new HTC Guide application method is handy, but forgoes the important step of disabling all other 3rd party applications)