Like a lot of underworld theories, it gets a lot of print but it's never been definitively proved. I certainly find it very plausible as once Genovese was out of the way, Gambino really had no opposition as far as underworld supremacy was concerned. Couple that with Luciano, Costello, and Lansky still having enough connections behind the scenes to set up Vito, Carl very well may have just taken that and ran with it, despite Vito helping him out with the whole Anastasia deal just two years prior.

Keep your friends close but your enemies closer...