Will we encounter random NPCs in caves, and if so, will they always be hostile or can we encounter other types of NPCs like archaeologists, geologists, or something like that?

To begin with, the NPCs will probably be hostile NPCs only, but for the future they want some caves to be inhabited, and for some caves to be in a state of being explored. Luke adds that they record dialogue for all of the NPCs, and it's okay to do that for a set of enemies because they're going to say and do many similar things, whereas non-hostile NPCs (such as archaeologists) will say something different, look different, move different, and because of being in development they don't want to go too far down a path (involving actors, cleaning up mo-cap, etc.) at this point in the game; they want to get a good solid first iteration working before trying to do any of that.