I've been looking into using another language on the robot along side Java as well, primarily for autonomous scripting. What I've found is that since FRC currently uses a Java ME environment (the Squawk JVM is J2ME CLDC 1.1), disappointingly most of the new cool JVM-backed languages are not compatible (such as Scala, Clojure, JRuby, etc). There are a couple of J2ME implementations of Lua floating around, but I was not able to get any of them working for FRC. It seems folks have more success with this from the C++ side of things with projects like RobotPy and Greyhound Lua. However, both of these are intended as a full replacement, not to be mixed and matched with C++ [citation needed].
There is always the possibility of writing your own scripting language, which would probably be a beneficial experience in and of itself. Additionally, Team 4334 created a scripting language called
Gordian designed specifically for FRC; you might want to check it out.
As was already stated, using a different language on the driver station or whatever you are using for vision processing will be fine.