Is it ok if a co-pilot is holds a camera for example while a plane lands, pointing it at the instruments, zooming in on the runway etc?
No it's not.
As for the weather conditions, a landing on limits and on a wet runway is part of the job and probably happens far more frequently than passengers realise. I personally wouldn't be overly concerned about lightning seen in isolation,
but I'd be more concerned if the various factors start lining up - the lightning, the weather radar "picture" that you see early on in the clip, the report from a previous aircraft......all sorts of thing that might be happening in the clip
And quite what possess pilots to put this sort of stuff "on-line" is beyond me.....