WHY IS THERE A FLAT EYE TUBE HEAD JIG AND A VERTICAL TUBE HEAD JIG AND DO YOU RIG THEM DIFFERENT?

Google "Stupid Tube" rigging. It's the way I rig regardless of the eye. Works great.

I assume when you say flat eye you are referring to the line tie being more in front of the jig. My guess is that works better for a dragging presentation vs. The vertical line tie. That can be dragged but lifts the butt of the tube up when you do that. The other keeps the butt down more.

Personally I have caught on both but did notice the difference playing with jig heads I own.

I've used both

One is for jigging, the other is for swimming

darter heads are generally used for suspended fish in the finesse world but line tie for jigs is an important aspect to how you fish them and what baits, kind of of complex but a swim jig has line ties more in the 30 degree angle and a darter jig is good for darting action and action on the fall, not for swimming a tube in my opinion, I use a slider jig head to swim a tube or peg a bullet weight