It tries. Accelerometer-based positioning is best used with camera displacement, which isn't used in Google maps driving mode (though there was? Is? An experimental on-foot mode that showed directions in AR).

the accel-based positioning I'm pretty sure is implemented app-side, not os-side, but I could be mistaken.

Probably not. Maybe to like know where you are turning in a round about. But the drift is too big to be useful over any distance.