[Snake]

Boxer:
- Korkenzieher

Martial Artist:
- Peddling Wheel

Firebird:
- Falcon Strike
- Swooping Stroke

I think those are all that proc damage under the enemy's location (and thus activate Snake Dancer), and not from where the attack is being made from. If anyone finds out others, be sure to post below. I believe this is in Balance-Fu so we can discuss if it's necessary or not.

But the answer's quite obvious. Positioning is a part of SL2's combat mechanics, and it shouldn't be cheesed because of how skills work, code-wise.

[Shujin]

As a Side note:

Peddling Wheel and Falcon Strike do not attack the tile they are standing on. they attack from behind.

That made Peddling Wheel always pretty unique in how it works, so I would like to keep it for that skill atleast.

You can try turning your back to someone who is falcon striking you, with Eviter or Cobra, it can proc then. Its because the attack is made after you are repositioned.