Zabbix Template for a Pi-Hole Server
Download the template and import it to Zabbix Server. It's for 7.0+. It's simple though and should be fine to backport.
The template just grabs the output of pihole status, parses it to JSON, and alerts when DNS isn't running or blocking is disabled.
Apply the template to the Host running Pi-Hole. Modify that server's Zabbix Agent configuration to include the following line:
AllowKey=system.run[/usr/local/bin/pihole status,*]
I run Pi-Hole on RHEL 9.4, and I don't remember having to make any SELinux policies.