To say that there is NO arc FLASH hazards associated with any type of transformer is ridiculous.While neon trasnformers are designed to have a high output voltage with a low output current to light the required diameter tube, they still have the potential to arc and flash. While it would be extremely uncommon for a neon transformer to flash, it is possible under the right circumstances.
More commonly, they're extreme fire hazards. I think that a certain level of arc flash prtotection should be used, not necessarily for the flash part in which there would be hot spewing metal flying but rather for the purpose of the transformer/ GTO wire arcing to the operator potentially causing the material worn to combust.
It also depends on the style of transformer as well. Smething like a Ventex transfomrer which has no secondary terminals exposed and a GFI built in has ALMOST no chance of flashing. On the other hand, something like Frances
P5KA2NG style transformer has a removable cover and requires you to expose the inner workings of the transformer to diagnose which has a MUCH higher chance of flashing.
I highly doubt anyone here would put there face next to a neon transformer that you have to service/diagnose and say "it won't flash". :grin: