This is all because of ED not having a working data-tape for the F-18.
Pre-planned, and known ground sams/radars (from whatever intelligence source, not real time) are added as positions in the HSD pre-flight on the tape.
To simulates that, if you remember, ED had all ground stations magically appear in the F18 HSD, as if they were added to the data tape pre-flight, unless the option to hide them was selected in the mission editor. It is possible to hide them from the HSD with this option.
Join a mission without that option, and voila!, you can magically see all the units. And because that is core DCS mission editor code, it affects the Jeff the same way.
They aren't simulating complex data-links, its just a mission editor option.