In version 1.9 of the join plugin the join projects are also listed in the downstream job list. They are not marked special. Is this O.K. for you or would you need some other representation?

Wonderful! I've upgraded my plugin... now if we can just get all of these pesky builds to stop...

I restarted my Hudson last night. I don't see any info about join on the downstream list. Hmmm...

The join job is on the downstream list of each intermediate project. Just think about the join diamond from the confluence page of the join plugin. If you want to see the whole dependency graph just go to
http://your-hudson-instance/dependencyGraph/graph

This is basically why I was asking. So you want to have a link from the split project to the join project without going via intermediate projects.

By the way: All this works only with hudson 1.341 or higher

There is a minor bug with in combination with the downstream build view plugin as you can see on the attached screenshots:

You can see the join job under every node of the downstream tree but only one of them is recognized as being run. The others are gray blinking balls with "NOT BUILD" annotations.

I know about the issue with the downstream build view plugin. Basically, the stuff the plugin shows you is what really happens: There is a dependency from each intermediate project but only the last one says: OK, build the join project. The other ones realize that there are still some intermediate projects to build, so they do not trigger the join project.
What would you expect the downstream build view plugin to show?

@ssplett: By the way, what downstream build view plugin are you using? When I tried this with the stock one, the parameterized builds where not shown in the downstream build view: see JENKINS-5761.