Cosidering the answer given below to Atis teleport question can you shoot when she / unit appears if you are in overwatch:
"The answer is YES!
Atis' teleportation is a form of movement, so you are allowed to shoot her unit it overwatch after she teleported".
Therfore can units in overwatch shoot at units who appear on the battlefield either through pre determined deployment zone's od drop point, in effect they are "appearing" on the battlefield without moving onto it.
You cannot shoot Atis in overwatch when she first appears in a deployment zone. Fighters in deployment zones are considered having already been there.
However, you can shoot her in overwatch as she comes in through an access zone (she cannot teleport since she wasn't on the battlefield) or a drop point (she wasn't on the battlefield and cannot move anyway).