What type of spoke failure are do alloy nipples cause according to these people. Spoke failure at the threaded area, at the elbow, or somewhere in between. Do they claim the alloy nipples cause spoke failure by increasing fatigue or from exceeding the spokes tensile strength. It's alwyas easier to have a debate when you identify the actual point of disagreement instead of talking about generalities.
I've never had a problem with spokes breaking on my wheels and I always use alloy nipples. You can acheive all the spoke tension you would ever need with alloy nipples so that's not an issue. If you want a theory that supports the use of alloy nipples here is one I read in the Barnett's manual. In the event of an object getting caught in your wheel the alloy nipple might break before the rim cracks potentially saving the rim. Kind of like a break away derailleur hanger. If alloy nipple failure is the concern then just use slightly longer spokes so that they are flush with the top of the nipple. The spoke will support the head of the nipple preventing the area with the screwdriver slot from collapsing in. As far as the alloy nipples stretching (or more likely not stretching)and causing a problem doesn't make sense. Spokes are supposed to stretch so why shouldn't a nipple and what would be the problem if the nipple didn't stretch. Some spoke stretched is a good thing. The flex that is inherent in a spoked wheel is why they continue to be used for bicycles and off road motorcycles.