It might be legal, but if found out it would almost certainly get their motion denied, which is why Apple aggressively pursued a statement from Samsung about whether or not they knew. As a result, Samsung has made a declaration they did not know, and so at this point if it later turns out they did now, they're in trouble.

More wise would have been just to remove him from the jury during jury selection. Overturning a jury's decision is pretty rare.