Not sure what the Ark team did or other games, but if the EULA says nothing against it, and you are not charging for you game then, it should be “OK” in the legal world. just have to keep things secured at all times, so hacking and related no no’s don’t get out in the wild.
But in all this should be a O.K.
As I do not work for Epic and do not have a legal background, I would still double check the EULA again to be sure how you plan to go about the design for the plugin.