There was a rumor online earlier today about a possible three-way swap involving the Nationals, the White Sox and the Diamondbacks that would send Edwin Jackson to Washington, Adam Dunn to Chicago and prospects to Arizona.

Huh? To quote Ross Perot, buddy, that dog won't hunt.
I understand that there are some in the Nationals' front office who are enthralled with Jackson, but c'mon, now: Edwin Jackson, though only 27 and having thrown a no-hitter this year, doesn't appear to be much of an upgrade over the pitchers already on hand or on their way back to the big leagues from rehab. I just can't imagine how they'd sell a deal like that to the fans.
Jackson is a .500 pitcher with a career ERA of almost 5 runs a game (this year it's currently 5.01). His best year was 2009 when he went 13-9, 3.62, with a pretty good Tigers team, but they didn't hesitate to trade him in that three-way swap with Arizona and the Yankees. Beyond the no-hitter he hasn't exactly torn up the NL; his overall numbers aren't quite as good as Rodrigo Lopez's for goodness sake, though with Dan Haren traded to the Angels, he may move up a slot on the Snakes' rotation - unless it goes to Joe Saunders. He does throw very hard and accumulates the K's, though his post All-Star performance has been dismal. There's a reason he's already with his fifth team.
I seriously doubt Dunn's wearing anyone else's uniform this season, but I've been wrong before. A Dunn-Jackson swap makes no sense to me at all, unless Adam's already agreed to come back next year.
And I don't think they actually allow that kind of deal.