It’s not clear from your question how the UE4 content interacts with the non-UE4 content. It sounds like you’re having people create maps in UE4 to be used in a non-UE4 game, but that resulting product is still a Product as defined by the EULA because UE4 was used (in part) to make it. So a royalty would still be owed.
Also be aware that something called Map Editor sounds like something that would qualify as a Engine Tool as that term is defined by the EULA. In which case, special distribution restrictions would apply.