That's definitely an interesting thought, but with his contract, Dempster would only be valuable if he was still pitching very well. There's no way Hendry trades him in that situation.
A friend spreading false injury rumors would be pretty unnerving. Either way, your case is pretty speculative. It seems more plausible that the team was less than forthcoming, especially in light of the very slow pace the Cubs took with him.
Walker wasn't a full-time player in 2004, and the knee injury early in 2005 was from a collision with Carlos Lee at second. His playing time these past two seasons isn't really the result of being injury prone.
You can't really mispell a personal name. People come up with lots of creative ways to spell names... Shawon Shawn Sean Chone etc. Yeah, but only one of those four was creative enough to spell it correctly.