The CWBP world map is a community effort so your welcome to add to it. The world of art is licensed with a 'creative commons' type - see http://creativecommons.org/about. This means that you may use whatever you like from it and would not need to ask permission but there are a few conditions. The CC license is of type NC-BY-SA so that means Non Commercial - i.e. you cant sell it. BY is attribution so you should say where you got the map or who made it. And the SA means Share Alike so that if you use the map, modify and then present a new map based on these then the new map must also be CC licensed with the same NC-BY-SA where you should quote the original author and you add yourself to the list of contributors.

So if you want to make a mod for Oblivion and the terms of using the Oblivion editor don't compete with these restrictions and you don't mind making it and sharing it in this way you can do so and you don't have to get permission for any of the people that made the originals.

It would be nice to just be able to say here's a map, do what you want to it but public domain stuff has a tendency to become accosted by companies with enough money to keep lawyers and the works gets absorbed into their portfolio. When you have a CC licensed paper trail of the work then its much harder to do that and there are entities like the free software foundation and EFF which will fight for the works to stay free.

So CC licensing is a way to state that this work is free and its going to stay free. Its a kind of guarantee that you have the permission to use it and share it safely.

So really its down to the Oblivion editor licensing terms as to whether you can make a map that's free. If you can do what you want with any map you make with it then you can, if they restrict what you can do with a map made with it then you cant. If by copying a CC licensed map into Oblivion then Oblivion have rights to it then that's against the terms of the CC license.