Sort of, white plymouth rock and white cornish, I believe.
But you will not get a typical Cornish X like the chicks sold for meat from buying these two breeds and mating them, even assuming I have it right. There are years and years of patented breeding involved in producing those chicks. And they are not the same from all sources. Hopefully some others who know more about breeds and genetics will chime in here.
Well, you said Cornish hens and I just assumed you were asking about Cornish X, the usual meat chicks. You can buy Cornish birds from Ideal and I'm sure other hatcheries. Believe Ideal has white cornish and dark cornish.
If you want to butcher a "cornish game hen," like the ones in the grocery store, and have a small bird dressed out, I believe they butcher cornish cross hens at 4 to 5 weeks old.