Is JDK 1.6 supported in IBM POWER 9(AIX 7.1-7.2)?
The Java SDK on AIX page has a section named "Java SE and IBM WebSphere Real Time minimum AIX support levels" that shows the minimum level for JDK 6 as AIX 7200-00 and AIX 7100-00.
Of course, AIX 7100-00 service pack support ended in November of 2013, so you'd want to make sure you're on a currently-supported version (e.g. 7100-05). Also note that AIX 7200-00 service pack support ended in December of 2018, so you'd want to get to 7200-03 or newer.
As an addendum, I'd point out that Oracle has declared that support for version 6 ended December of 2018.