Off the top of my head, I would say no. The savage will have more flexibility, but the rigidity of the plate would serve to impede the savage. You can't bend a rigid target.I don't know where I stand on this either. I'm just pondering. Right now, I'm going with RAW. But, I wonder...does a savage wearing a loin cloth have an advantage grappling a foe wearing a rigid breast plate?
*Yes, I know size modifiers are probably going to influence grapples more than ACP. However, I feel that adding ACP into the mix is just a bit too much.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.