Hi Kai,
Nothing really to suggest - I think I would use the same workaround as you.
UPD: Ops, yes, if the category is hidden, then people will not see its title, unless they are assigned to the site level. I agree, it should be noted as a bug. I have assigned users to such role on the category level - and its title is still invisible. I guess can create sub-category in a category and put courses there.. Then they will see it
P.s: You can even skip creating a separate role altogether, assuming you are not adding people to roles on the site level. If your student role is overridden to see hidden categories/courses in the category, and you add employees manually to courses there as students, then they will be the only ones seeing those courses.