Not really sure we should be advivating the "Its okay as long as you don't get caught" legal theory....
The whole point is that Bethesda (and Hasbro of course... did anyone mention that legally he should get permission from Hasbro as well?) would not mind if you want to have a bit of fun with some friends, without stealing or taking advantage from them in any remotely meaningful way (if he wants to make a Fallout Monopoly then he most probably owns a copy of both)... I bet they have more serious things to do than to worry what that one guy will do this weekend, ask them and they will say no though, because they have to as Gizmo said...
There's no ethical dilemma here... come on!
Legal conditions are often extremely absurd - for reasons that can make sense but still...
For example I think that if you buy a movie on DVD you are legally allowed to watch it buy yourself only, watching it with a friend is forbiden... Technically that friend "steals" the movie by watching it for free. And that makes you a pirate.
But you wouldn't seriously take that into account, would you?