It should work. It's something that I did several years ago around Java3. I've made sure it has worked with every Pharo release (the tests pass under Pharo3). I will look into why they are failing under pharo4.
It's a project I did because I was mainly doing Java and go frustrated with serialization errors and it just went from there. The classloader and decompiler were for my own edification. I used to have it working inside the inspectors in Squeak, but I doubt they work now. I've been meaning to work on it again.
Everything should work. I did start on being able to Java VM code inside of Pharo, but got sidetracked with work and life.
I'd be happy to talk more. It's been about a year since I last looked at the code. I'll dig around sometime soon.