That is probably the single most important utility of the old grid type bore sight devices (we actually called them "collimators" back then) - making sure the scope cross hairs are properly oriented. I've lost track of how many rifles I have seen with crooked scopes.
The vertical tang sight is a different story, though, at least the ones used in long range competition. With these, we actually mount them at an angle to compensate for "spin drift" at long range. If the rifle has a right hand twist, we lean the sight to the left, if it has a left hand twist (pretty rare) we lean it right. Mine are all tilted about two degrees left, established by a lot of shooting and trying.
Doing this keeps the windage more zeroed as range increases and the rear aperture climbs farther up the sight staff. "Spin drift" is more of a visual representation of what is going on here than it is an accurate terminology. Imagine a bullet "rolling" in the direction of the rifling twist. If a tall long range sight staff is truly vertical, we could run out of windage adjustment, even on a calm day, as the bullet "rolls" or drifts in the direction of the rifling.
Here is one of my long range match rifles, a C. Sharps '74 in .45-2.6". The aperture is set on about its 200 yard elevation. At 1,000 yards, it's most of the way up that staff. With about a two degree tilt to the left, when the aperture is still centered on the windage scale, the rifle is still hitting center on the target. On a calm day...
