I have experienced several excellent caddis hatches on a certain east Tennessee river that is known for good hatches of Caddis. When the hatch comes off really good, the surface of the water, in certain places, can be littered with caddis fluttering and drying wings before take off. I've witnessed them on the surface for a minute or longer before they take off in flight. And the resident trout go nuts, feeding on them on the surface like mad.
I have witnessed this first-hand, many times, and would respectfully disagree strongly that trout rarely feed on caddis on the surface.