Brisket bark is not from sugar more than it is from pepper and coarse salt from what I have noticed. If you put other spices in yoour rub, it will be in there too, but just a simple coarse salt and pepper rub will make quite a bark by the time the brisket is done. I think the fact that the coarse salt remains on the outside shows that it is not going to make the brisket salty. Now, if you put a finer grained salt on first, like the seasoned salt Donnie-Pitmaster-T is talking about here, that stuff is gonna get sucked right into the meat, along with the flaovrs of the rubs. Heck, now I'm repeating what Donnie already said.
In short, coarse salt and black pepper makes a mean brisket bark.