Dogs do not normally pee in their sleep. If this is happening there is a health issue such as a bladder or urinary tract infection that requires treatment. If not treated, these infections can be lethal.
I have a lab, and he never peed in his sleep. The second he woke up, though, he was ready to go.
He's 15 months old now and before I let him out to go to the bathroom, he eats his breakfast and has some water - so he's all ready to go #1 and #2 right afterwards.
I don't think they do.. I think they act just like babies do. They wake up for like 2 seconds, pee, and go right back to sleep. If they are peeing at night, they may need to be taken out in the middle of the night. That's how my 8wk old beagle mix is. we are sometimes up with her twice during the night to take her outside. Good Luck! Hope everything works out!