Try this: 
 
  Run traceroute on your ubu box to first determine if you are getting data from your ASA: 
 
 tcpdump -vvv -i  src host  and udp port 514  
or   
 tcpdump -vvv -i  src host  and tcp port 514 
 Assuming you see data, then move on to the next steps, else you are either not sending logs from your ASA, you have a routing issue (which I doubt as you are able to ping your syslog server), or are perhaps running SELinux and are blocked? 
 If you see data, then your issues are with either your syslog-NG daemon, or its config, most likely its config. 
 You need to have syslog listening on the appropriate protocol, dependent on whether you are sending to tcp or udp; you can listen on both for syslog-NG.  Also, aside from a listener, you must objects such as source, destination, log, filter, parser, rewrite rule, or template. 
 If you see data in tcpdump, then copy/paste your syslog-NG config file into this issue, please remove your comments. 
						
					
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