Yeah, the basic concept behind both Vader's suit and the Stormtrooper armor is that they were meant to work in a vacuum. There even is some concept art (and now, action figure) of Luke donning a breathing mask. There's a scene shown in some concept art as well of the Vader and the troopers actually flying through space from the Destroyer to the corvette, but that was dropped in favor of the ship doing a locking on thing. Probably wouldn't have worked on SW's limited budget, and would've required wires and all that.
The prequel EU seems to state that there's some kind of HUD in their helmets, which are the forerunners of the later suits. Also if the armor was originally designed to counter droids, maybe rebels are a more random target since they're mostly humanoid.