Bully sticks will absolutely help keep your dogs teeth clean. Simple fact being that saliva is a dogs natural way of cleaning the bacteria off of their teeth, chewing a bully stick causes them to have more saliva in their mouth and for a longer period of time (because they are continually chewing on something).
My smallest one, Jesamine had the worst teeth when I got her and she loves to chew bully sticks and her teeth are a million times better than what they were before I got her!
I attribute this to her love of bully sticks and chewing them often and the fact that I do brush her teeth. All of my dogs chew bully's and get their teeth brushed with C.E.T tooth paste and their teeth are in great condition!
Also, if you buy bully sticks that are not smoked they shouldn't smell as bad. I get mine from www.bestbullysticks.com, they have all kinds of different sizes and types there.