I gained some info on this the hard way back in 1999. I was working on the helpdesk and we had scripts to run as root to create new users. I was on the main DNS and NIS master for a 5000 person division of the company and the user creating script hung up. I did a "jobs" and found my script was job 1. So then I did "kill 1" forgetting that to specify a job number instead of PID you need to make it %1.

My session closed immediately and I couldn't log back in. I quickly headed toward the Unix admin's area and found one of the senior admins walking at a near run toward the server room. I hollered "Hey Dan", and without breaking stride he yelled back "WHAT DID YOU DO???"

He got it fixed fairly quickly. In the elevator on the way back down to our offices I said "Consider it a test of your slave server setup." He didn't think that was too funny.

Thus I can tell you for sure you can kill process 1 as root on Solaris 2.6 and 7 and it will crash your box. It will trigger a reboot if your auto-boot? in the OBP is set to true I believe. I'm pretty sure the protection to prevent that was included in Solaris 8, but it may have been 9.