To answer the original question...yes. There are a few OCs in the league who are also QB coaches...I think Cam Cameron is one for Baltimore. That's just one example. I don't know of any DCs that pull double duty and it's extremely rare on the defensive side of the ball.
As for those two guys coming onboard and doing it, I think it would be highly unlikely a first time coordinator would try to pull double duty. But I have my doubts that either one of those guys join us, even more doubts any coach from Green Bay joins us jsut becaue of their "unwritten rule".