Right now the documentation is very sparse. What you are already looking at is pretty much it. I figured most of it out looking at the network traffic while playing with the console.
The gwt-server is a combination of two components. One being the bpm console that is for both Riftsaw and JBPM. This code can be found at https://github.com/bpmc/bpm-console/tree/master/server/integration/src/main/java/org/jboss/bpm/console/server/integration
The second piece is the actual jbpm implementation which can be found at https://github.com/droolsjbpm/jbpm/tree/master/jbpm-gwt/jbpm-gwt-core/src/main/java/org/jbpm/integration/console