Not all of them. As a defensive end, you rarely, if ever, have to cover. Thats the hardest part of the transition for DEs, and LB's going to DE have a similar adjustment in always facing linemen right at the snap.
There have certainly been many instances, but one I've watched is Andre Carter. Twice has he been on a team thats gone from a 4-3 to a 3-4. No one is going to dispute that Carter is one of the better pass-rushers in the league, usually good for at least 10 sacks, but he's just not a fit in the 3-4 and will struggle.
Might that be Mario Williams? Who knows...........but to say that 4-3 ends always translate to 3-4 OLB is not a smart statement to make.