I was catching up on the Huskers N Side shows last night and ran across a segment that pretty much verifies what we are having our LBs do.
Riley was diagramming our defense and showing the run fits. He talks about all the defenders 'finding their gaps' so that the RB will get tackled in "whatever gap he takes." Also says guys have to "stay in their gaps."
So it's pretty obvious that our run defense it based on having a defensive player in each gap and that player is (basically) only responsible for that gap. That would mean LBs are not supposed to flow to the play but fill their gap. That would also expliain why they aren't making as many tackles as it perhaps seems like they should if they are more responsible for filling a gap than getting to the ball carrier.
Here's a link to that segment