I shoot Scottish Football with my 1Dx (soccer for our US friends) not paid work or anything, just for a Football website and I shoot in Raw. I intend giving jpegs a go at some point but as my deadlines are not immediate I use Raw. I spoke to a experienced Pro Sports Photographer earlier this year and for football he only shoots jpeg, he's a Nikon user. He doesn't have the time to process and convert after a game when he needs to get his images to agencies/newspapers quickly, within 20 minutes or so, in order to sell them. Lets face it Newspapers dont need the highest image quality for the printing quality and size they use, online versions may have changed that though.
BDunbar's comments are interesting as I need to experiment with the set up for jpegs. As a Club photographer largely doing landscapes for comp entries I have never once shot jpeg since I converted to Raw around 4-5 years ago. There is absolutely no doubt for my Football shoots that jpegs are the solution, most of Studio1940's reasons above explain why but I suppose one can become too reliant on the convenience of Raw editing in Lightroom. For me its a confidence thing in not shooting jpeg.
In answer to the original question, 1Dx and mostly jpegs, cant see why not, thats what most Sports/Press photographers will do, who I'm guessing are the largest %age of owners of the 1Dx.