No, you can't. If you try to run the RFA Java 8.0 library with JDK/JRE 1.6, you'll encounter java.lang.UnsupportedClassVersionError: <an application class name> : Unsupported major.minor version 51.0.
Note: major.minor version 51.0 means that the library was compiled with Java 7.
Actually, RFA Java requires JDK/JRE 7 (or higher) since version 7.4.
Hope this helps.