Offically supported environments (OS) for mackerel-agent installation are described on the following page.
Apart from monitoring by installing mackerel-agent, you can also use plugins. One of Mackerel's official plugins is mackerel-plugin-snmp.
mackerel-plugin-snmp - mackerelio/mackerel-agent-plugins
Using this plugin, it is possible to monitor network devices etc. from a server installed with mackerel-agent. Please refer to the above README for more information.