I think you may misunderstand Vert.x's polyglot features:
While vert.x supports many programming languages, all of these are run on the JVM runtime. This means when you use the ruby vert.x API, you're using JRuby; likewise with Javascript run through Rhino, Python through Jython, and Groovy/Scala run through their own interpreter/compilers.
That said, it would definitely be interesting to see the performance implications of using one of those languages and vert.x on the JVM.