This returns data:
index=jenkins_statistics (host="jenkins.host.com" )
when I add eventtag=jobevent, that field does not exist on any of the records from Jenkins.
Running Splunk 6.5 and 1.0.4 of the Splunk App on a Heavy Forwarder and Search Head
field event_tag should be extracted at index time on heavy forwarder (if you installed the app on heavy forwarder and using the default source type), could you check the sourcetype by
index=jenkins_statistics "job_event" |stats values(sourcetype)
it should be json:jenkins.