At the VERY least, he would provide LB depth, something that is always good. aLso, if Dallas is intent on bringing in old veteran LBs, I would much rather it be Ray Lewis instead of some guy that hasn't played since 2002 and has been sitting on his couch ever since.
Even if his play time is limited, he will add aggressiveness to the defense when he is on the field. He is a firecracker, and only needs a small spark to blow up.
Our current defense is good, but is too sleepy. The players tend to react instead of making a play happen. My stomach hurt when I saw a lesser defense talent wise (IMO) in Seattle dominate Carolina with its aggressive play. Those guys made plays instead of waiting for something to happen. That is the kind of defense that wins championships and Ray Lewis is a player that can bring that fire to Dallas.