Two things to check:
1. Is the Orion syslog server listening on UDP port 514
2. Does a packet capture show ssylogs reaching this system?
If you want to test the syslog message locally, you can download "Log Forwarder for Windows" in any of the windows server on the same Orion datacenter location and test the syslog. If the message is works then look your firewall.
This is an obvious one but I assume that you've configured your solarwinds server as a logging host on the devices?