They use doubles all the time in Hollywood. As it was, the cast spent hours and hours on the set just getting done what had to be done by them personally. When you see a back-and-forth conversation, for example, they have to film it more than once--from over each actor's shoulders. Sometimes, they even use doubles for that. Remember when Kate went in to do her Admiral Janeway scene in "Nemesis"? She said she was flattered that Patrick Stewart bothered to come in and do it with her personally instead of just adding his responses later. She expected to be talking to a "stand in" when she did it.
That's the way it is on film. They have to reset the lights, check the sound, make sure no one left a Coke can somewhere, etc. So when they have a quick scene where someone is pushing buttons or, as in that picture, adjusting a robot, or, as Sue Henley said, shooting a pool ball over and over again, why put the actors through it? They can film it with a stand in during post-production, a few days or weeks later once the cast has gone on to another week's episode, and just put it in as they edit the show.
Perhaps it is disappointing to know that many (read most) of these shots are not the "real" characters' hands or shoulders or legs, etc., but that's the way it is.
Sorry.
I'm confused. 
Sue mentioned that she was the Janeway standing, so the Janeway on the ground must have been Kate.
This wig is dreadful, isn't it?
