Are bullets still dangerous on the way down after they have been shot in the air?

Yes, they fall, reaching terminal velocity they are just as dangerous and kill many people a year. In Turkey last year a young afghan sheikh killed his father doing this on his wedding actually.

Danger is a relative term.

The bullet is a lot denser than ice which makes a hail stone.

So they have a higher terminal velocity than a similar mass hail stone.

The bigger the bullet the higher the terminal velocity. And the heavy bullet is more dangerous due to its mass alone anyway.

So at one extreme you have an air rifle pellet that is hollow and not dense. It has a low terminal velocity and would be hard to be considered dangerous.

At the opposite extreme you could have a cannon shell. Which would be dangerous even if you simply dropped it on your foot.

And in between you have many different bullets with many different degrees of risk.

Yes, they are still dangerous. It doesn't happen very often, but every year or two around Christmas and New Years Eve there are cases of people being injured (and sometimes even killed) by bullets falling back to earth after having been fired into the air.

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that depends on weather or not they are shot over a densely populated area. their lethality is apparent regardless. as to weather or not they are "dangerous" depends on the likelihood that they are actually going to hit somebody/something.