Being assigned a vampire for a roommate isn't what he was expecting, in all honesty. He's more than a little cautious when it comes to vampires (bad prior experience. nothing against Jamie personally, evidently). And well, up till now, Jamie hasn't tried to attack him yet, and talking to him doesn't seem to feel like Yamato talking to someone evil, so Yamato will most likely give him at least a little benefit of the doubt.

He appreciates the effort, so really, the only courteous and probably decent thing to do is probably to at least play along with dodging the massive elephant in the middle of the room that is Jamie's current state of vampirism. "Yamato. Nice to meet you, too. So, uh. What do you do?"

Okay, so it may or may not be a liiiiitle bit awkward, still, at the very least, he's not being antagonistic or anything like that.