Well I am a new owner of a Rott myself and she is only 6 weeks, so I haven't had the chance to raise or train mine yet but my sister-in-law has a 1 1/2 yr old male (Cain) and new people come in and out of her home all the time. Not relationship wise but freinds. Your boyfreinds dog sounds like he might be a little aggressive period. Cause Cain never offers to bite anyone or any other animals. He runs from my 6 week old puppy, but he would protect his owners if needed. I think I would want to know the history of how he raised the dog first. Cause I was sceptacle about getting a Rott cause I have a 3 years son and did not want to take a chance until I feel in love with Cain and my son plays with him and Cain loves him. When he is outside playing Cain is sitting right there next to him and followes him everywhere to make sure he is ok. I knew that depending on how the dog is brought up is how it is going to act around other animals and humans. Just get the background on the dog and make sure that you keep a good distance with the dog and the children at least until you can trust him.