First off, Dramamine affects different people in different ways. Right now i dont think there really is anything that says you cant take it and dive.. I have taking it(non-drowsy formula) myself on boatdives (as have my friends) and had no negative side effects diving down to a max of 65 feet. But is it the way you want to go? I doubt it. Because it is a chemical introduced into your body and at any given point on any given day you can get a side effect. I had taken dramamine before so i know exactly how my body reacted to it. You should know the same.
Now thats out of the way, I got motion sick a few times while diving at first. I have never gotten sick to the point of puking, but i felt crappy in my head. The first dive i figured it was because of how different you see things under water it kind of disorienting, also if you are doing extrenous things it will heighten the effect if you are prone to it. I just took a step back, slowed my pace, relaxed myself and it went away. Second dive was great... The next 2 dives were good, water was calm and no problems. A few later i got it bad because i was fighting a current, i was swiming next to a wall at around 60 feet lookin down for a floor that was around 160 feet and i stopped, relaxed again and told my body we need to end the dive. When i got home i felt so bad. I was really motion sick, my head was killing me and i felt ill. My wife reminded me that i didnt eat at all that day, it was the late afternoon, and i was in less than ideal sea conditions. After that i never had a problem again. My body got used to it, i set a proper diet for my dives and now im fine in no matter what the sea conditions. The point of this story, well you gotta figure out what works for you, but using dramamine all the time is probably not the best idea, at least for you bodies sake. Good luck.