I'm not sure exactly what you are asking. However, the biggest difference in evaluating 3-4 linebackers to 43 backers is that, well, not many college teams run a 3-4 defense.
Let's start with that. You are generally looking at college 4-3 defensive ends and projecting their move to a position most haven't played. So when you're watching film you're trying to watch their first step, change of direction, quickness off the ball, and, if you're lucky, you may see them dropping into coverage. But for the most part everything about coverage that you see is without pads in worksout.
When you do get teams that run a 3-4 defense, you've got to identify if the backers are actually doing a good job or if the offensive tackles, or offense in general is a little slower in comprehending what they are seeing because they don't have a lot of experience seeing that.
In the 4-3 defense, even in college. Most linebackers you can see drop in coverage, shed blockers, fill gaps and everything needed to evaluate them