It's impossible to know whether Randall, or Lureen for that matter, is complicit in or aware of the identity of those guilty of Jack's murder. If I had to say, I'd assume Lureen had a good idea after the event; for Randall, I guess, it came as a frightening shock.
But he's in a better position than say Ennis would be - he could move elsewhere and get another job as he has relevant qualifications. And as long as LaShawn sticks around, he has his camouflage in place. He might be more circumspect in making propositions in the future, though.