Pass rush is not considered at all in determining the coverage grade. Their is a seperate Pass Rush grade per player, per team.

If the pass rush forces out a quick inaccurate throw--that will not help the coverage grade. The coverage grade doesn't care about the result of the throw, just how good the player was in coverage on that specific play. Trying to isolate how well that player did their job on the play regardless of the other variables around them.