First off, a great article, I recall when it was first published on Discus Holland, and then later posted on cichlid-forum. I was a mod on CF at the time and I recall finding it odd that African cichlid keepers didn't connect the dots to S. vortens, and what is commonly referred to "Malawi bloat". Probably due to the fact that in Africans HITH is seldom an issue, most fish severely infected die long before pits in the head surface. Again, a great article for 15 yrs ago, one of the best out there - but red wigglers in my opinion are a bit of a red herring. I have never seen any type of study to back up such a claim. Outside of their circle of discus keepers in the Netherlands, I have never heard anyone with a scientific background in this field speak of such a thing.
I think that the red wiggler comments are best described in that articles end note section, where the authors state: "Consider experience - never underestimate experience, it is a vital ingredient in any rational justification for diagnosis, prognosis and treatment etc. However experience should always be tempered with scientific rationale and never followed blindly."
To which I doubt that one will ever find any scientific data to support the red wiggler theory. Years ago someone in the Netherlands most likely believed that they had found a cure via the nutritional aspects of worms, and ran with it.
Experts in this field do not advocate feeding red wigglers to treat S. vortens and/or Hexamita.