Oleg: IMO this meta issue is a bad idea. We're likely to only get comments like John's here.
John: The Jenkins process' JVM and the javac process are independent, so you should be able to run Jenkins with Oracle JDK/JRE, and build with J9 (except with Maven job type, maybe). Also, most or all of the issues seem to only apply to the Jenkins master. Try running the master on another JDK, then add a slave running J9. Also, possible solutions are best discussed on the jenkinsci-users mailing list.