ever is a strong word. I know that at the moment they use some parts of OpenJDK 7, but If they need to comply the Java (tm) caused by licensing, they will be forced (sooner or later) to actually don't use a deprecated JVM. As I know OpenJDK will be depracted on 2024. so it will take some time, but it will come.
According to Jake Warton, they only cherry picked some parts of OpenJDK 7.
From the commits they also don't appear to ever fully support Java 8, only lambdas.