I think your wife might be on to something there....
What you mean is: "can dogs move their eyes up from the horizontal in their skulls?". I'd always (foolishly) assumed that this pig/dog question allowed the animal to move its head.
It could well be that they can't move their eyes that way in their heads -- lots of animals have limited movement of their eyes in their sockets. What kind of dogs are they? Some short-faced dogs have very shallow eye sockets which might complicate things.
On the other hand, it may be a psychological restriction -- what about if their heads are restrained, such as when poked through a hole?
I had a dog once which could just get his nose through a cat-flap -- that would have been a good research position, if I'd have thought about it at the time.
It could also be a coordination restriction, like the one which prevents us while awake from moving our eyes so they diverge significantly, or pointing one up and one down -- there's nothing physical preventing this, but just try it! When asleep our eyes wander all over the place, like David Blunkett's.
Now I've got eye movement as well as colour vision to research in my cattle....