Adding the oil cooler doesn't void the warranty according to the Kohler representative I spoke with. Actually, they sell them to those individuals who would like to buy one.
As for the reason why add an oil cooler?
Well, Kohler puts them on their Command engines and
because they say it lowers the oil temperature by as much
as 40 degrees.
Why would I want a cooler running engine? Because it is not uncommon for the ambient temperature where I live to reach 100 degrees during the summer.