In OSX, look for the this folder /Users/{USERNAME}/.jdeveloper/system{VERSION}/DefaultDomain/bin
Edit the file setDomainEnv.sh and look for SUN_JAVA_HOME and make sure the value is the same value as your JAVA_HOME, i.e. /Library/Java/JavaVirtualMachines/jdk${JDK_VERSION}.jdk/Contents/Home, by default it seems it is set to an empty string "".
Edit the file startWebLogic.sh and add the following before setDomainEnv.sh is called.
JAVA_VENDOR=Sun
You can test it out by running sh ./startWebLogic.sh, if it runs with -jrockit error, then all is good :)
I've also tested with Java JDK 1.7 and it seems to work.