No. Not inherently.

It's worth doing a pressure or leak test on something you're uncertain of, but it's not likely to be an issue.

A lot of times this can just be from dust buildup on/around that nozzle (I'm almost sure that's not the proper terminology tho). An easy thing to try is shutting off the gas to the insert and taking a can of compressed air to that nozzle and everything around it. If you can easily take off the panel in front of it, even better, spray all the dust out you can.

Is this dangerous?

The hissing noise is not. Turning your pilot knob to some in-between setting is.

I know nothing about the systems in question, but it seems the "hiss" is in time with the flame changing shape. So, perhaps a blower or valve turning on/off, open/closing.

Again, I know nothing, but if it's a sound from the equipment turning on/off, I don't think it would be potentially hazardous. Probably very annoying though.

Is it a thermopile millivolt system? I just fixed mine last week and when it was hissing it was because I lit the pilot with the grub screw too wide open. There’s a tiny little brass screw that is right next to the pilot control knob that allows you to adjust the pilot flame size to get the right coverage on the thermopile.

Of course it could also be dust.