But there's a chance that any survivors learn to hide from planes and you've now given an evolutionary pressure to cows to hide when hearing airplanes or helico

But there's a chance that any survivors learn to hide from planes and you've now given an evolutionary pressure to cows to hide when hearing airplanes or helicopters. Along with that a pressure that makes the ones that blend in less likely to be spotted to be bombed. So yes, you're right you probably won't get cows that can survive napalm itself but now you've got cows with camouflage and an instinct to hide.