I had the same problem with the Cisco Security Suite. (https://splunkbase.splunk.com/app/525/)
Everything was installed and setup correctly but the dashboards always said "No results" or "No data". I found a fix for it when looking into why the "Data Summary" button on the search page was not showing the cisco:asa source type. Long story short, for some searches, not all indexes are included by default. New/created indexes, by default, are not included. So if you followed the Cisco docs and created an index called "asa_syslog" you need to add that index to the default search list. This is also true for other created indexes such as "oswinsec".
This is set in Setting>Access Controls>Roles. Select the role that your user belongs to, in my case admin, then click the "Indexes" tab. Enable both the "Included" and "Default" checkboxes for the index to make it searchable by default. After I added the index I went back to Cisco Security Suite and the dashboards populated immediately.
Can you attach a screenshot of what you are of the dashboard?
Try going to Search and Reporting, then clicking on data summary to see if your devices are sending syslog data. If you see the device IP address or hostname, click on it and then see what kind of source or sourcetype information you are getting. You should see udp:514 or whatever port you have configured for your network devices to send syslogs to.