Personally, I feel that grappling a WCV is just... an awful idea. Especially Raiths.
Cop grapples WCV(Raith) to the ground, finding her extremely hard to hold down, he uses his body weight to pin her. He then starts trying to put hand cuffs on the... beautiful... *drool*... soft... Yeah... yeah right. She couldn't have him MORE where she wants him.
But anyway, GM adjudication. I doubt that grapple blocks ALL action. That's not reasonable.
Then again, the rules aren't perfect.
The way the book describes falling damage would make parkour and Jackie Chan both completely impossible.
So... personally, I'd assume that it blocks physical actions, but even there, that there is some room for common sense rulings.
If my group tried to use a grapple on a Raith, that'd be a mistake.