[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.