agree that it should be, not saying that it would be a fair judge on every sack, but it would show basic competency over the long run.
I have a DE as well, and have seen my player chase the QB into someone else's arms. That guy shouldn't have really gotten the credit for the sack, or that specific lineman the Sack Allowed stat, but in the long run it is a good tool since it happens both ways.
If it's an individual stat, it should only be if the guy you are covering makes the sack. Nothing you can do if you're on the other side, or busy blocking a DE and the SS makes the sack.