I personally don't have parry leveled, but I highly doubt it, as shield, evasion, and guard all increase the rate.
Again, to really see a diff, you have to whore the guard in virtually every slot.
Try this, I've always believed it was compared to the mob's combat skill (which is why it's easier to get a decent rate on lower end mobs).
If your parry is capped, gear parry and go try it out on some lower level mobs.