What is this with people always assuming Zenimax / Bethesda would C&D everything? I am not exactly the biggest fan of them, but damn, their stance towards modders really is very positive. As far as I can remember, the only project where they asked modders to stop was that Morrowind to Oblivion port. Here the modders copy&pasted all of that stuff over to Oblivion, which obviously is not ok. Especially if this means that Morrowind won't be required anymore for playing the game.
In any case, if in doubt there is one simple rule: Don't post about your mod over at the Bethsoft fora. Then the moderators don't have to remove your stuff and tell you to please stop.
As for the Fallout stuff: We worked on FOnline since 2009 and never in all the years we heard any complaints from anyone over at Bethesda. It simply didn't matter for them. But if you ask them first... Well, chances are high that they prohibit it, because that's what they need to do to keep their property and copyright stuff in line.