I have 2 bull mastiffs... When I brought my daughter home from the hospital my mom was scared to death they would hurt her and wake her up constantly.. They are great with her first off but we did watch them close at first. She is 19 months now and they let her roll and climb all over them and are so good with her. You will have to see how he does at first and go from there. As for the barking mine bark loud!!! And like previous poster said baby is used to hearing her bark because he can hear inside the womb. It is muffled but he can still hear. Time will tell but they normally adapt and learn to protect instinctively.
My mom had the same issue with her min pin. We were all very concerned that she would bite or something. When my brother was born the dog instantly loved him and protected him and his toys. They can sense that this human is apart of you. I still wouldn't leave them alone together but I'm sure there isn't much to worry about, and with the barking the baby can hear it in the womb and will be use to it. My brother would sleep thru my dog barking even the bigger ones