I'm not sure what you meant by "There doesn't seem to be a Java DCE implementation anymore (JADE seems to have disappeared) so writing DCE integration isn't likely. "... Afaik, DCE is just a name we use at Pluto and nobody else uses it, and we never had java integration. So I'm not sure what Java DCE implementation there ever was.
However I assume the purpose is to be able to use Java devices on Pluto. All devices communicate via sockets, so you wouldn't need any Java implementation in DCERouter. Rather we would need a Java socket library that sent messages in the same format as the C++ socket library. DCERouter wouldn't care who formed the message, as long as the format was the same.
The class which encapsulates a message is "Message" in the DCE/Message.cpp file. It takes the message and converts into a binary data block, which gets sent to DCERouter on the socket. So if you had a Java class that did the same thing as the C++ Message (ie a Java Message), and then another Java class which would open a socket connection to the router and send the message, then that's all that would be required.
Does that make sense?