I think with any "car" type tyre you're going to see positive camber relative to the ground when a car rolls to the outside.
If you had perfectly equal length upper/lower a-arms, if the body rolls outward in a corner 3 degrees, the wheel/tyre will roll equally outward at the top creating positive camber.
In un-equal a-arms, the compression of the outside suspension in a roll creates, as you've said, negative camber relative to the car. But relative to the pavement it helps counteract positive tilt out at the top during a body roll turn. This helps keep the tyre flat on the pavement.
But for normal driving I doubt either would be much of a detriment to tyre wear or handling.
I think you'll find almost every car on the road without McPherson struts will have shorter upper than lower control arms, or un-equal length control arms.
