Dodging isn't blocked by a grapple, movement is blocked by a grapple in my opinion dodging should probably require you to be able to move which is why I find the fact that grapples don't effect dodging weird, the same as if someone tried to parry with their hands cuffed behind their back.
Aspect tagging is the way to go, probably aspects like "helpless", "held down" or "Human (replace to fit) Shield" would work.