This whole "eye sockets" thing is very strange. Cameron introduced a new alien with holes now on the side of the head. Now if we look at the skull in P2, those wholes seems to be the eye sockets who moved to the side of the alien head for some reason. I believe that this is reinforcing the theory of the dome is only there to protect the head while its forming and morphing under the dome, wich will then slowly melt and reveal the "true head" of the aliens.
As for the alien's vision, well... I don't know. The sockets sure don't have anything to do with it. And I'm not too sure about the sonar theory.. We saw what seemed to be the alien's vision in A3, but that kind of vision would not work without "eyes". Wich the aliens don't have. And if by sonar, we're talking about something similar to what we saw in the movie Pitch Black, then no I don't think that it's the way they see. Seems to be a little too restrictive.