Most Cisco Nexus can only send syslog data over port 514, if you have more than one type of device that is limited to port 514. You could go to your syslog-ng server and setup iptable to redirect to another port on the server to monitor it. to setup iptables to redirect traffic from a specific host over port 514 you would need a command like the following:
iptables -t nat -A PREROUTING -s 10.x.x.x -p udp -m udp --dport 514 -j REDIRECT --to-ports 1234
Then you can set up your syslog-ng.conf to watch the traffic on the set port 1234 to have different source name
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