Since the CSV is much easier on pumps than any other type of valve, pump companies would also have to disallow warranty for using a Cla-Val, Watts Valve, Dole valve, or even just a ball valve, because the effect is the same. Pumps have been lasting for generations while being controlled by many different kinds of valves. Pumps companies would never disallow a warranty for using any type of valve, and in most cases, they would never know if it did have a valve on it.
Pump companies will disallow a warranty if the pump or motor comes back with signs of no cooling. It is easy to tell if the impellers or thrust bearing is toast, that there was a lack of flow condition. As discussed earlier there is no way for a CSV to cause a flow low enough to get the impellers hot. The minimum flow built into a CSV was derived from the amount of flow required to keep the pump and/or motor cool.
The only reason any pump company would try to make you think that they would deny warranty, is to get you to use their Variable Speed Pumps instead. You should be very leery of anything that the pump and motor manufacturer spends so much marketing money on. They are marketing the Variable Speed Pumps because they make much more profit. It is a high dollar, short lived product, that keeps the cash flowing at the big manufacturers. However, they make their profit at the end user and installers expense. The end user keeps having to purchase expensive and short lived equipment, and the installer takes the blame for everything that goes wrong.
Several major pump manufacturers have tested the CSV. They say that the CSV makes pumps last longer and use smaller tanks. So I know for a fact that they are doing everything they can to dissuade you and everybody else from using valves instead of variable speeds. And that in itself is the main reason you should be using Valves instead of VFD's.