Some users use monit to monitor and control some or all Pi-hole daemons.
A daemon restart initiated by monit is not advisable during a Pi-hole update/upgrade.
Therefore it should be a good idea that the Pi-hole update process stops monit before the update and restart it after a successful update.
Pi-hole does not ship with or currently support monit.
Yeah, this is out of scope for us at the moment.
Ok.
Just to be sure. What I mean...
Before 'pihole -up' starts the actual update process it stops monit (e.g. 'service monit stop') and restart it at the end of the update (e.g. 'service monit start').
There is no need to ship Pi-hole with monit, or to install monit during a Pi-hole installation.
Why not creating your own custom shellscript?
I guess it would be easier. Because some people use monit, others use nagios, others use zabbix ......