Other than the trauma of the surgery, I'm not sure the plate will affect him at all. The plate is a very thin sheet of anium that is wrapped around the bone at the point of the break, to reinforce it. It just lays along the bone, and doesn't interfere with muscles or tendons. I understand the new ones are really thin, and conform to the bone so much that it's almost like nothing is there.
That being said, if I had that huge gash on my hand, and had to go play a contact sport it would interfere so much I might just stay home and watch on TV.