Encountered Julian twice due to reloading an earlier save.
The first time as I was following Barstow Julian became hostile as I approached. I quickly killed him and I believe Barstow exclaimed something like "what are you doing?!" I'm not sure if that was directed at me or Julian. She then resumed her dialog that ended with the task of killing the rest of the ghouls.
The second play Julian became hostile almost as soon as I walked into the construction area with Barstow, before speaking with her for the fist time. I killed him and there was no reaction from her.
Reading the page for the quest A Model Citizen is appears my second encounter could be a bug. I myself was a bit confused because of Julian being a named character an I wasn't sure if he was in any way important to any of the VW quests.