In my opinion, both are different. It is not necessary that you will get a robot inactive alarm once the server reboots.
And robot inactive alarm can be a cause of communication errors between the robot and hub in addition to actual server down or errors with nimsoft watcher service. So robot inactive alarms get generated because of a number of different reasons whereas computer reboot just indicates an actual reboot of the server.
So it really depends on one's requirement if reboot alerts are actually actionable or not.
But in our environment, it really helps us in investigations and rca's to be true