We sadly do not know who exactly that made the old maps and we'd of course advise users to ask for permission to use them "if" possible, but it's not always that straight forward so we just leave the discussion open for now.
As far as the game goes, as long as the official games maps in the current version aren't tinkered with we do not see much problems with users modifying the game, as long as it doesn't change "how" the game works.
One big point in all this though is that we are not looking for repeating history with how FH+ came into play, and have several different versions that users expect us to monitor and take care of as the official game when it's not.