Because of the pressure differential against the windshield, you will need to worry about rain as much with a cowl scoop as a forward facing TA scoop, possibly even more so. However, the TA scoop isn't as bad as you might think. When your walking through the rain, does your face get as wet as the top of your head? No. The area of the scoop is relatively minor when compared to the frontal area of the car. By contrast, a cowl scoop pulls air from the base of the windshield. The windshield has a larger percentage of area of the frontal section and combined with its laid back position, will acquire more water on it than the front of the car.
Now, do they look bad, IMO, no. The base design of the R/T Challenger hood and 70 Road Runner hood have obvious hints towards a cowl induction look. But there area lot of mopar guys that think cowl scoops are forbidden on mopars and you'd better be prepared to catch a lot of flak about it. Given the popularity of cowls, it is also possible to get a taller height on them than with comparable 6 pac/ta style hoods, if that is a concern.
Heck, I might try a cowl scoop just to see how many people it does tick off.
BTW, have you actually found a bolt on TA/6 Pac style scoop? I'm not sure those exist, but I haven't done much digging around scoops in a while.
