Dude, it could just as well be a poor design. Just cause someone builds it does not mean they knew what they were doing. In aerodynamics, you'll find that even people with a large amount of knowledge have a hard time connecting the dots and coming up with solid answers due to the complicated nature of the art/science. If you have only seen one example of it, and the guy is not the one who won your class championship, I'd guess he either thought it looked cool, or, he has some theory he is testing out.
As far as drag racing aerodynamics in general, in my mind, I see it as a balancing act. Anything you put on your cars body is going to create some type of drag which will slow you down aero wise. But if you are able to create more down force with it, and can put more power to the tires, overcoming the drag and then some, then there is a benefit for you.
I think the trick is to create just enough down force on the rear tires to keep them from spinning at full throttle while going down the track. Too much down force is drag and slows you down, too little, and you spin the tires.
Directional stability is obviously a concern for safety, so aerodynamics can play a large role here if things get unsorted from mid-track on when you are at high speeds.
Here is a little reading I found for you, I'm sure what I'm saying is nothing new to you.
Aerodynamic Tips & Tricks from Hot Rod Magazine
Good Luck and be Safe!