Can I land Headshots with Ana?

I'm assuming you mean critical hits on headshots. There's no explanation other than no - she will not get a critical hit when landing a headshot.

Source: http://overwatch.gamepedia.com/Ana

Unlike Widowmaker, Ana doesn't seem to get any benefit from scoping, other than the zoom.

There is actually a benefit to scoping in with Ana. While she cannot score headshots, her projectile speed changes based on zoom. While scoped in, her projectiles are hitscan and cannot be deflected by Genji. When not scoped in, her projectiles have travel time and can be deflected.

(Hitscan vs projectile source)

(Genji reflect for scoped and non-scoped source)