Hi,
Did you format correctly your input in the Advanced Settings of the host?:
tcp://FQDN:514
tcp://IPv4:514
udp://FQDN:514
udp://IPv4:514
Where IPV4 or FQDN are the IP or FQDN of the syslog server
Does your user have the rights on the ESXi host?
Additionally check the following points:
1) Check if the ESXi host vmkernet port have an access to the syslog server
2) Check if firewall rules could prevent access to the ESXi host
3) Is this server, a 3rd party syslog server or is it the syslog server coming from the vCenter Installer CD?
Keep me informed,
Regards