I think most of us know What happened to fallout 4 capital wasteland and know that F4NV wont have that problem because they're are doing their own VA but this is my question:

Could Bethesda pull something on the project for having the story of the new Vegas?

as basically you will receive the story for New Vegas for free, doesn't the writing for NV have copyright or something?

Well, yeah. You couldn't just take all the dialogue from New Vegas and put it into a book (Falldown New Angeles?).

My understanding of what they're doing now, since they're giving proper credit and not selling anything, is that it's a legally grey area (same was true of using voice files but they didn't want to risk it)

Worst case scenario, they'd have to change the name and the settings is what I'd imagine.