Is there a tutorial or extra documentation on the Distributed Debugger?

First check out the document DEBUGWS.PDF that is installed with VAJ Enterprise Edition. The help system also has some documentation on how to use it; go to the Tasks section of the online help and look near the bottom for a section titled "Debugging programs using the distributed debugger".

There are also several articles on VADD that may help. The following page is a search results for the text "distributed debugger": http://www7.software.ibm.com/vad.nsf/SearchAll?SearchView&Query=distributed+debugger
The first match, A Distributed Debugger Tutorial is pretty good.