The fish are not exposed to ammonia at detectable levels with tank transfer.ime.
Uv may temporarily reduce bacteria concentrations in the water column, the bacteria equilibrate by growing more to take up the slack . In any case most bacterial infections occur and reside in or on the fish and don't see the inside of uv. IME,bacterial infections can occur but are not nearly as common as ich. They should be treated with an broad spectrum antibiotic in a hospital tank,; not with UV.
Tank transfer is only effective against cryptocaryon,which is the most common killer for fish. It may mitigate velvet which also has a free swimming phase but is not reliable for that since the life cycle of that parasite is much different.
It does not contribute in anyway to bacterial infections with careful fish handling and gentle capture. Beyond that I'll refrain from discussing treatments for other maladies since this thread is about the tank transfer method and cryptocaryon irritans.
Please, you know that ammonia is not good for fish. Why would you want to take up a position that claims a bit of ammonia is not very bad? The fact is that it can be very bad and the impact may not show months later.
This method has some features of the new tank syndrome. You expose fish to low levels of ammonia, not just a few days but repeatedly. Fish die months later in new tank syndrone.
This article should at least mention Prime or Amquel.
Ich is much feared disease only if one does not have the skill to comprehensively eradicate it. The method exist so there is no need to be concerned about ich.
About the UV on bacterial infection... many people do not know how to set up a UV properly, do not understand how it works, or have wild expectation about it. Many do not understand its limitations.
The UV is very important and I WILL never go without it for newly imported fish. Bacterial infection (to a lesser degree viral infection) is the most dreaded disease, since unlike ich, cure is not always effective.
The purpose of the UV is to vastly reduce the waterborne concentration of pathogenic bacteria and viruses. Why is this important? The immune system has two components, generally antibodies which requires previous exposure, and, white blood cells and the likes that do not require previously exposure. The latter's effectiveness is very much dependent on the concentration of the pathogens.
Ever since I started using the UV about 25 years ago, the incidents of bacterial infection has dropped by about 80%.
The UV is hard to understand so many people miss its benefits. The UV's impact is not absolute and sometimes it does not work; this makes it even more elusive. We are talking about percentage of chances with respect to the UV on bacterial infection.
The UV destroys many drugs, so it is more preventive than cure.