I can't appear to directly trigger a workflow job from another project with Trigger/call builds on other projects in the Build options.
In the multijob case after configuration the workflow job is not listed in the dashboard for the job - and the workflow job is not triggered. For the freestyle case the workflow job is not run either but it does return the following error:
Yet the MyWorkflow workflow project is clearly available.
I'm assuming this is just not something that is yet supported by the workflow plugin, but it would be nice if it were.
In the meantime I'm working around the problem by setting up my jenkins server to point to localhost as a remote jenkins server and triggering the workflow job as a remote parameterized build. This seems to work, but I lose the context of triggering the job directly within another job.