>Does this process really produce no UV?

I have no idea, but the microscope he's looking through could certainly have UV protection built-in. Or perhaps the pulses are so short and small that the cumulative risk is negligible?

Either way, it seems to me like there could be ways for it to be safe enough to require minimal PPE while still producing some non-zero amount of UV.

I'm also thinking about skin exposure. Fortunately glass optics are at least opaque to the most dangerous bands of UV.

the microscope blanks when the arc is fired

What happens if one time it fails? Does it instant blind?

Auto-darkening welding masks block UV and IR all the time [1] so you're protected against things like arc-eye even if it fails to darken. Also, masks generally fail-safe (to darkened, e.g. for flat batteries) and presumably this welding microscope is designed to the same standard.

[1] https://youtu.be/qMyeVXuElkQ?t=333

Looking straight into a welding arc doesn't blind you instantly. Eventually, sure.

More rapidly it gives you a lingering after image and feeling like your eyeball is full of sand

the 'eyeball full of sand' can last for several days, and really interfere with your normal functioning. that and the greatly increased acceleration of cataract development means really dont look at the blue light.

oh yes, I can see where my comment might sound like I'm saying it's ok to look at the arc; it's not. It's just that it won't blind you right away