Moisture loss is directly proportional to the final temperature of the product. If you cook super hot, the outside areas of the product will get to a higher temperature before the center gets to the temperature you want. Those outside areas that get to a higher temperature than the core will tend to dry out.
However, in barbecue, you are usually cooking your meats to a much higher internal temperature than a steak. Evaporative cooling actually slows the temperature of the outside while the core is coming up to temp. You simply can't get the internal temperature of the meat above the "stall" until enough moisture has evaporated unless you wrap. So, it really doesn't matter what temp you are cooking your barbecue at (within reason), because it has to get rid of the same amount of moisture before it can beat the evaporative cooling. Of course, if you wrap, you are avoiding the stall. However, the temp inside the wrap is never going to rise much above the boiling point of water; so you're cook temperature doesn't matter that much.
So to make a long story short. Hot and fast vs low and slow doesn't make much difference in meats where the target temperature is above about 175. As long as it spends enough time in the zone to render most of the collagen into gelatin, you'll be fine.
