Hello,
SCOM can monitor CM, Server OS, database, etc.. If you were trying to alert on diskspace issues you could have SCOM look at the CM database and use that HW inventory data.
Zabbix.The inbuilt Windows monitoring template will catch the basics (cpu/mem/disk space/etc). We have custom templates to pull information from the various Log files, registry keys, perfmon, WMI and Powershell scripts for more detailed monitoring of the SCCM MP and DPs.