As has been said many times, here. Ferrari won't care. Ferrari is Ferrari. It has no peers. McLaren tries, but a McLaren is still not a Ferrari. Marchionne hisself said that he would not let one sibling dumb down another. Ferrari has said as much. Ferrari isn't run like the rest of the F-C stablemates, it gets its own special place, and consideration, and is almost always left to its own devices.
Ferrari could care less, if the Viper makes more power than anyhting in its stable. Heck, if it did, they would probably assist in helping it to do so.
The Viper is a huge engine. It doesn't need a lot of the fancy stuff to make big power, it does it with dispalcement. It carries its weight a lot lower than a 4VDOHC engine. It doesn't need 4 valves or DOHC, or a lot of that stuff. It uses dispalcement instead of these complexities. It is LOTS cheaper to build. IT doesn't need to rev as high. The Viper is good road car, but it does not have what a Ferrari has for the simple fact, that it isn't a Ferrari.
Does a Ferrari buyer buy a Ferrari, AND A Viper? Sure. Does a Ferrari buyer buy a Viper INSTEAD of a Ferrari, not really. At least Ferrari isn't worried.
Ferrari has never been about making big power numbers. It is about making the cars they want to make, in order to fund the race efforts. Google wiki. The Chrysler Hemi's were making more power in the 50's than Ferrari was making at the time. Ferrari wasn't worried then, they are not worried now.