There should be no problem in term of byte code compatibility but I can foresee turbulence with libraries like the ones that are now part of the JDK, or even if you have JavaScript components, with the replacement of Rhino by Nashorn.
If you ask, I reckon you have a Mule app running on 2.2.1-HF5 so why don't you try it? Start your app, run your regression tests and report your finding here, as it may help others.
Cheers,
D.