If your cam is going to be like a 420 HP cam which is a good choioe from what it sounds like then stick with the wet exhaust. With the wilder cams and tighter lob sep like 110 and under you can get what you hear alot about on this board is reversion. The overlap from the camshaft (from tighter lobe sep. ) causes or tends to suck the water back up into the engine from the wet exhaust. This also depends on what kind of exhaust he is thinking of getting also. If he likes the throttle lube (beers) most certainly stay wet to keep the law away.
I hope I explained this OK.