Since they are not limited by a single threaded VM, you would run those using the worker pools and communicate with them via an actor type model similar to erlang. So, modulo a small amount of verticle code to deploy your image processor, yes.
Not automagically, but java has some really good tools for helping. See the http://docs.oracle.com/javase/7/docs/api/java/util/concurren... package. Check the Executors section and you can easily distribute work via threads to all your cores. In fact, vert.x is using netty, which makes heavy use of threads along with async IO. You can do both.