Tom - Of course. To be clear - the ball is a digital level, with respect to gravity. The output is displayed not as a number but instead as the ball's deflection.
So, if the ball is deflected when you're on the ground and still, you either have an ADAHRS that is installed with some roll error in a perfectly level airframe, or perhaps a slightly non-level airframe (tire pressure? the ground underneath?) with a perfectly-mounted ADAHRS, or something between the two.
In the air, note that a slightly out of rig or out of trim airframe, even if it's perfect on the ground, can cause some actual bank/slip in the air. This would be displayed by the attitude display / ball as a small amount of bank and ball deflection.