I am having a little difficulty understanding you.
I tried creating a project from scratch, neither of those fields are working. Its possible that I don't understand how they are to work, but I can get a regular FK to work just fine.
What exactly do you mean by "linked in the wizzards?" In a regular FK, for example, If I wanted to link to a category table, I would just drag the category table to the foreign table field. The joomla users table is not listed to drag.
In this next image, you'll see that when I drag any of the subfields, for example, "username" to the view, I still get the "Joomla user > Last visit date" instead of username.
Is it possible, that we simply do not have have access to the joomla user table?