Where is it evident that Don Vito even KNEW that Carlo had beaten Connie? After all, it was Sonny alone who discovered the "first" beating, Connie begged him not to do anything, he mentioned getting her to a doctor & then beat the crap out of Carlo. The beating could have easily been hidden from Connie's parents.
As for Vito involving himself more w/ the Connie/Carlo marriage, that's not what this story is about. Women have no place in the "business", and neither do their husbands, which is why the Don graciously provided Carlo a living, but nothing more. If Carlo married into the family only to become one of the "boys" (which I think he did), then he was out of luck, and it was just another indication of how stupid he was.
Nancey