Well, all right. I stand corrected. There is indeed a site owner. named “monitoring” in my case. 
However I still cant get the agent to run on home assitant side:
<<<check_mk>>>
Version: 2.1.0p20
AgentOS: linux
Hostname: a0d7b954-ssh
AgentDirectory: /etc/check_mk
DataDirectory: /var/lib/check_mk_agent
SpoolDirectory: /var/lib/check_mk_agent/spool
PluginsDirectory: /usr/lib/check_mk_agent/plugins
LocalDirectory: /usr/lib/check_mk_agent/local
FailedPythonReason: