43 OLB's are much easier to find than 34 OLB's are and you don't spend the resources on them that you do for the pass rushing OLB's. The big money goes for the pass rushing DE's in a 43.
That's why you always saw Jimmy Johnson drafting DL in the first round but only once (Robert Jones) did he draft a LB in the first round... and Jones was a MLB.
Think Charles Haley and Tony Tolbert going after the QB with Dixon Edwards and Vincent Smith in coverage.
We already have two very good 43 LB's in Lee and Carter. All Dallas would need to do is get one more starter and they'd be set barring injuries.
Actually, in last year's draft, Bobby Wagner would be a perfect example of a move they might would make to fill the third spot. Wagner is the guy we supposedly would have taken out of Utah State had we kept our 2nd round pick. He's fast and aggressive, but isn't a pass rusher. We would use him in a 43 scheme the same way Seattle is. He would be a perfect fit with Lee and Carter.
A second is about as high as I could see us going on a LB... unless there is someone who they think is just head and shoulders above the others in round 1 (maybe Manti Te'o). But a 43 OLB just isn't as much an impact position as a DT or DE is, so that is much more likely to be the first round pick if it is on defense.