The short answer is no.
However, I need to qualify my answer, because unskilled, indiscriminate manipulation of the neck can be dangerous … and they are not the same thing.
The question is like asking, “Is electricity dangerous?” If your house has been wired by a qualified electrician - and if you don’t so anything silly like sticking your a metal fork into the outlet - then electricity is a safe and powerful force. Now, if you decided to wire your entire home because you watched a few Youtube videos - or if you go outside with a metal rod in your hand during a thunderstorm - that is a completely different situation.
There is a big difference between risk and risky. Risk is inherent with everything that we do. Even crossing the street has a certain amount of risk associated with it. However, risk is not the same thing as dangerous.
So, when an upper cervical adjustment is given by a qualified upper cervical doctor of chiropractic - a professional who has years of training and advanced study - the procedure would not be dangerous. Granted, there is a small amount of risk: about a 5% chance of an adverse response such as headache, sore muscles or short-lived dizziness, and maybe a 0.00002% chance of severe adverse response. But “dangerous?” No.
On the other hand, having your buddy twist or “crack” your neck without any proper training … that’s not just dangerous: that’s stupid! And that is not in any way, shape or form the same as an upper cervical specific adjustment.