I have tried to set up a "SSH Agent" and they are mostly running fine, but there is one issue which makes them useless.
If for some reason the connection fails e.g. the user account on the host expires or changes password, the ssh agent item will go into unsupported state and no trigger can be created to catch this. This means that the zabbix users must actively monitor for failed test instead of relying on notifications.
Putting severity to blocker, as I am blocked from using "SSH agents"