Jack, I've heard the story of Gen. Wheeler saying that too. I can't think of a reference off the top of my head but I believe it does have at least some measure of truth to it. It may have been due to a fever he was enduring. I also believe that he was asked to serve for the reasons you mention and that there was concern what the reaction of the Southern people was going to be when once again they would see the "Yankee" army driving through the south. It is my understanding that many folks were pleasently surprised to get the warm reception they did as the men made their way to south to Florida and on to Cuba.
Gary Busey played Gen. Wheeler in the Turner movie, Roughriders. How accurate the portrayal was I don't know. Tom Berenger, who played Gen. Longstreet in Gettysburg plays Teddy Roosevelt. I enjoyed the film a great deal.