By fiddling with the bracket (provided it's a clamp-on, not a frame boss), you can adjust not only the alignment, but the pressure that it places on the tire. I don't know if it makes a noticeable difference, but I set mine up for the minimum pressure at which the little wheelio would still spin.

Dynamo hubs definitely have more resistance when loaded. I don't know why this would not be the case with bottles.