Graylog Special Agent

Hallo,
what does the graylog check do exactly?
I ve a rancher2.3 setup but logfiles checks via ELK or syslog aren working well,
Rancher 2.3 has a graylog output option and my idea is to check if I can see more output using this way.
Is it possible to check the greylog for recorded events like failed logins?
Thanks
Ralf