Can someone tell me what these are?

Since steel is underneath the chrome, I see no reason why the holes couldn't be welded up and then smoothed with a grinder. I would be careful about how you remove the old chrome around the holes, because chrome is very nasty stuff. You would NOT want to inhale it in either powder of vaporous form. I'm sure your guy that rechromes the bumper will know the answers and he can weld up the holes.