Syslog logs configured properly:
Are not visible at the backend SIEM
Release : Any
The syslog is generated and sent as soon as the event occurs.
As far as the setup is done properly it should work, there are not registered bugs at any time for the same.
Take capture on port 514 while performing some changes or forcing some event to occur for the syslog to register it.
The capture should display the packets the proxy is sending to the SIEM