Our usage is very similar with Kiwi as the syslog intermediary for SCOM.
The legacy solution is a VBscript that formats the message then calls EventCreate. This allows us to specify the source and event ID but not custom logs. The 'new' solution is a Powershell script that will create the event log if needed and write the event.
Both are more complex than necessary and fairly expensive computationally since they have to shell out but it works. I would definitely prefer to have the functionality in the Kiwi engine itself.