If I were you, I would seriously consider moving out or, having your doper roommate move out. Dealing drugs only leads to one thing: TROUBLE. I would most definitely distance myself from this person.
VERY General and broad answers to your question:
"If my drug dealing roomate were to get arrested or our house was to get searched, could any of us non-drugdealing roomates get in trouble with the law?"
-- Depends on overall circumstances. The police, for all you know, could be investigating your roommate's dope dealing activities. Assuming IF roommate is indeed being investigated, the police could obtain a search warrant and search your house too. So, where could that potentially leave you and your other non-dope dealing roommate? In the middle and answering a LOT of questions. Sure, you both could eventually be cleared of any wrong doing but again, depending upon the circumstances at hand, you both could also end up getting handcuffed and taking a trip to the police station! Definitely NOT an ideal situation to find yourself in!
Bottom line in my book: I think your doper roommate is an a$$hole and a fool to be dealing in the first place AND, putting both you and your other roommate possibly in Harm's way. Dealing dope sometimes can bring with it a lot of potential trouble. (i.e.: Mad customers, roommate may owe people money who have guns! etc.). What kind of a person potentially endangers others.
I don't have all the answers to your situaition but I maintain my suggestion: At minimum, I'd defintely move out or get him moved out and go your separate ways ASAP...
"Good and evil are present in this world, and between the two there can be no compromise" - President George W. Bush, in his farewell address to the nation.