I find it depends, but mostly the ADFs will go to the surface to grab food. I used to think not, but I have seen otherwise.
I occassionally feed my ADFs freezedried tubifex worms (in thos little cubes) in a clean glass baby food jar, turned on it's side at the bottom of the tank. After a while of the frogs going at the cube, they often knock it out of the jar and the remaining food floats. My frogs have no trouble going to the surface to eat the food. I am not sure if they would go up for it if I just plopped the food at the surface though. Probably, my guys are out within a minute of my putting the food in the tank. They also enjoy shrimp pellets that I feed no and again.
\Dan