I wonder how many NPCs share the same voice actors

4

More than people would like.

BGS has never done a great job of providing variety in terms of voices for characters. Outside of main characters, I'm expecting a lot of repeats as was the case in Skyrim and Oblivion. Perhaps since VO is so important in this game though, maybe BGS made more of an effort to give us the impression these NPCs actually are different people with different voices.

Least they can do is hire voice actors who can change their accents or their voice. Hearing the same person for different people was enough to drive one nuts.

I have the game, from what i can tell all essential npcs sound different. Raiders and enemies alike however are all but probably 2 voice acters.

About as many as can tell us about the Mojave, gambling, and nuclear winters.

I'm certain they will be just as abundant as in Skyrim...unless you play a localized version.

I imagine its about the level of skyrims voice actor pool

Already I can hear the same raider voice on that ghoul piratey character in the trailer. I expect lots of repeated voices but that's OK considering how large a game world they make.