To clarify:
An engine plugin uses the GS plugin sdk which allows you to call engine functions (like beep(), ent_create(), diag() etc, also user defined lite-c functions) and read/set engine variables (like fps_max, entity->x, ev->pd3ddev etc) inside the dll. Of course you can achieve the same with a normal dll and transfer those GS specific stuff from the dll side to a lite-c file, but this normally results in messy and uncomfortable code.

As i've written above, it was possible to use engine plugins with the free edition in A7.82 and even before with the atari lite-c version. I don't know and i don't care when exactly this was changed, they removed a (for me) essential feature.
Normal dll still works using PRAGMA_API, but maybe jcl just forgot to disable it in the last update?