Problem here - if you're grappling your bodyguard, your bodyguard is only delaying the inevitable as they are unable to counter-attack. Furthermore, your bodyguard is typically faster and stronger than you, so good luck grappling/holding on to him (or her).
That said, whether you or your hostage get hit depends on a roll like anything else, as far as I can tell. So let's say you're fighting Super Katana Man and you've hired Super Katana Girl to protect you, if you grapple Super Katana Girl all you're doing is keeping her from attacking while you take stabs to the face due to Super Katana Man's super katana skills.
Not to mention, why not just grapple your enemy if you're that much of a pro grappler?
Anyways, that's not really what I was suggesting.
You ever go out, and see some cockbag try to assault a friend of yours? You ever put yourself in the middle? That's what I'm talkin' bout. Never had a friend grab me and hold me so the guy assaulting him could punch me in the face. I think you need better friends :P