Oliver says HELLO ROOMIE! Since Dominic is another sexy addition to the Dorm of Sexy Evil, he'll fit right in. Oliver would enjoy him immensely, seeing as Dom is another person to add to his 'people I don't manipulate for kicks' list. They'll get on fabulously, I'd wager.
Casey and Gwen might know him through classes, but neither would really pay him much attention. I imagine that both would be pleasant to him should he speak to them though.
All of my sixth years are oblivious as to who he is! :(