> Am I correct in reading the license in Github that this is all GPL? Albeit GPL2 but still not some Oracle proprietary license.

Ref https://github.com/oracle/graal#license, appears that the parts you would want to distribute have the classpath exception which allows linking without messing with the license of your code (same as the JVM). The FAQ also covers this: http://www.graalvm.org/docs/faq/.