I think this article should be in the "Usage" section for DataIntegration and not in the Enterprise DI, even if you happen to be using Enterprise
You can pass java objects from one job to a child job IF the child job is not running as a separate process. If it is a dynamic subjob, it is always a separate process.
So, for a tHashOutput, I think you could pass it to the child job but I don't think you could make a tHashInput read it, because you can only make the tHashInput read it, so I'm not sure how you'd get at it. You could probably use raw Java and get at it, but at that point you might as well just create a Map with java in the parent job.
Does that make any sense? If not let me know. You definitely can create any HashMap, etc. with Java in the parent job, and, so long as the child job isn't a separate process, pass it into the Child job.