Nintendo only cares when you try to enter their exclusive bubble of 'casual/family games'.

If you're outside of the bubble, you pretty much have nothing to fear. WoW has had fake Pokemon for over a decade and as far as I know never got any problems.

Stick your finger in the bubble, though, like so many fan game devs have been known to do, and you're very likely getting it bitten off.

Pocket Pair thought they could hide from the beast inside the bubble. They're probably going to be eaten alive.