RFCE has some new terrain types, like moorland. I don't know if that would lead to any conflicts. You can try to copy the BlueMarble.fpk to RFCEurope and see what the result is. At worst, it doesn't work and you delete the file. I expect that all vanilla terrain types will be blue marble and all new terrain types will have the current art. (If blue marble also updates terrain features, it will have the same result)
It is only a bit copy-pasting. Download this modcomp and install VD manually. (
https://forums.civfanatics.com/threads/welcome-to-dawn-of-civilization.533861/, second post. Just unpack VD in the mod folder and replace everything) Then open the VD_CIV4CivilizationInfos.xml (Assets/Modules/Varietas Delectat/XML/UnitArtStyles&CivInfos) and copy all new units and buildings from the original CIV4CivilizationInfos.xml (Assets/XML/Civilizations) to that file.