If it is connected to the Internet, then I guess the kernel needs to be hot-patched need to be applied to avoid security issues.

Were hot kernel patches available ten years ago? I remember some company who did this (for Linux), and it was quite a while back, so it's possible. But I doubt it was mainstream.

I recall long ago that SunOS boxes had to be rebooted for kernel patches.

I don't remember about Solaris.

I'm not familiar with other Unices.