Well, the bottom line is that although the bowler probably doesn't know the ball is out of spec, it is HIS responsibility to use legal equipment.
I don't think I'd file a protest over his performance last night, but I would take him aside, and say that "several people" had commented on the ball layout. Was the ball really that mismarked from the manufacturer - or something like that. That will give you a chance to find out what he knows about the ball and the layout. If he's unaware, he'll probably respond with "what do you mean" - if he's aware, he'll say - oh yeah, when we weighed it out the cg was off...
The tactful approach. If he then doesn't get the ball checked, THEN I'd bring up the negligence aspect.
I have one ball that's borderline. It has about 1/16th of an ounce less than legal top weight. I was told this by the driller at the time he drilled it. I was told to be very careful when weighing in at the ABCs, because they could find it illegal. I was also told that if this happened, to have it checked at multiple stations...