I haven't driven Road Atlanta, wet or dry, but I've worked corners there for four years and I've seen it in every weather condition except ice, including fog so bad the corner stations couldn't see each other. The nastiest wetness that I'm aware of is
a) The hill from T11 through T12 ... if it rains a lot, the water can actually "sheet" down the hill, crossing from driver's left just past the T11 station across to driver's right near the bottom of the hill. It's like a really wide, really shallow river. When the light is right, it's really visible.

T5 ... a small river forms from up near the track-out rumble strips near the T5 station, down the hill, across the apex of T5 and back over to driver's right before running off the track at the bottom of the rumbles on driver's right just before turn in for T5
c) T10a ... not much in the way of rivers, but you're going really fast, you get a little light as you come over the hill at T9, you're braking about as hard as anywhere on this track, and for a long time, and you've probably got a couple of cars around you ... luckily, gravity is going to give you a grip assist at the bottom of the hill, but maybe after you've initiated the turn in
d) Occasionally, under really heavy rain, you can get a little "streaming" down from T4 through The Esses ... if it's wet you've pretty much got to tiptoe through The Esses anyway if you don't want to visit us at the corners during the race
Up the hill after T1 doesn't seem to be much of a problem, and T2 through T4 don't build up water but it's tight and slicker than normal. The backstretch and the run from T5 to T7 don't seem to be much trouble. T7 has more fun than normal due to the extra slickness, the camber going away from you after the apex, and the inevitable spray of mud on the surface as the day goes on.