The link only recommends them for Alpha rims. AFAIK, They’ve only been doing Alphas since after Paligap have become the importers. I may be wrong though, so won’t be offended to be corrected!
I can see the sense in it though, although only really for aly nips, and even then the weight of an aly nip and a copper washer probably isn’t far off a brass nip, but with none of the durability.
In any case, if we’re willy waving, I’ve built hundreds of wheels too, and repaired thousands more, and I’ve only seen spoke washers on a couple of really obscure branded wheels.