Yes, but the movie stills are shot so that you're looking UP at the Xwing (or at least level with it) so you can't see if there's a droid socket or not. At those angles, unless the droid was stll in the socket, you wouldn't be able to tell if it had one or not.
Not really - look at the CGI mockup shot. You can see that the droid's head actually raises above the cockpit frame a little bit (which is how it looks in the movies, and how our current models look). At least the front-angle shot of the partisan X-Wing lets you see a view that should have the astromech, if it was present.
And certainly the shot of the crashed ship would have it - from that one, you can see that there is not only no astromech, but there isn't even an opening for one.