Tons of UV, that's how legacy fluorescent lamps work, a nice intense UV flux excites the phosphors inside the tube. The UV can't escape the glass but the white light from the phosphors certainly can. Germicidal lamps use UV-transparent quartz.

As for x-rays the typical voltage drop across a long tube is like 100 volts, the whole point of a ballast is matching the normal hundred or so volt drop to whatever your local line voltage is using at a constant controlled current. Anyway the penetrating power of an xray is linked to the voltage drop, so it would be difficult even theoretically to generate xrays stronger than a hundred volts or so. So given that it takes 50 KV to 100 KV for a dental xray source to beam completely thru a head, you're looking at like a thousandth the penetrating power. Very hand wavy estimate that 100 volt xray source will likely not penetrate the glass and almost certainly not penetrate clothing or the surface layer of dead skin and skin oils.

The risk assessment for being nearby a heavy cloud of vaporized hot mercury would seem to imply the main risks would be biochemical in nature not physics in nature. Actually the most realistic risk is an economic death penalty if that leaks and requires hazmat cleanup.

Probably not mercury rectifiers or thyratrons, but hydrogen and deuterium thyratrons do (edit - emit X-rays, that is). They're much higher voltage devices. Example at [1]

[1] https://www.e2v.com/shared/content/resources/File/documents/...

AFAIK, x-rays are the result of electrons slamming into metal at high speed from a high voltage accelerating potential (>20kV). The glow inside Mercury rectifiers comes from ionization of Mercury vapor. Various other voltage regulator tubes glow from the ionization of low pressure gases inside the tube.

Common beam power tubes and power pentodes sometimes glow blue from residual gas in the tube even with plate potentials ~500V.