The kitten will not necessarily outgrow this habit unless you discourage it. I also had a kitten who loved to suck, particularly on human hands. He was orphaned at about 2 weeks and raised by me. I think kittens have a strong innate need to suck and they'll transfer this to a human hand, or a poor dog, if they don't have a mother. This cat used to suck on my hand between the thumb and pointer finger, and he did this all the time until he was about a year old. It obviously made him happy and I got tired of fighting him (he's very willful), so I let him. I probably shouldn't have because he's 5 now and still does it occasionally when he gets stressed out. My friends think it's hilarious. I guess it's like a security blanket for him.
This probably isn't good for your dog though, either emotionally or physically. Rescued kittens often suck on their smallest sibling and I've heard of people using a small amount of bitter apple to discourage it. I suppose you could use this on your dog, but keep in mind it'll also also have the unwanted effect of keeping the dog from cleaning itself because of the taste. It might be better to separate them long enough for the kitten to 'break the habit'.