This requirement has been in the README's for as long as I've worked with NBU (close to 12 years...) The idea is that the plug-in will be reloaded with the database restart.
If previous upgrades / patch installs have been successful without database restart, the same should apply now. I cannot remember any installation where the agent stopped working because the database was not restarted. I have noticed though the years that sometimes a patch update on Windows will ask for a reboot and sometimes not. We have always rebooted when it was required. Best to include reboot in change control - just in case...