Hemsky has been more offensively productive than Hudler due largely to better opportunity, but he is worse in every other area except skating. "I'll take an injury-prone quick skater, I think he'd do well on one of our top two lines!" Why not just put Hudler there? He's actually got proven chemistry with those guys, works hard, is capable of better defense, and has shown excellent offensive abilities. And he's NOT injury-prone.
Hemsky was signed to a six-year deal after scoring 154 points in 211 games over three seasons. This is compared to 84 points in 221 games in three seasons for Franzen. Hemsky got a six year deal, Franzen got an 11-year deal. If Hemsky were to play at 80% of his normal level in the playoffs, I'd say trading Franzen for Hemsky and Brule wouldn't be bad. They were willing to simply hand Brule over to the Kings, so he basically counts as an add-on in this deal.
Think about roles though, Hemsky was top six player for the Oilers, while Franzen was bottom six with the Wings. All his points came in a big push near signing that contract. Indicating that he would be a big time scorer. Whether or not that was wise isn't the question, I am simply indicating the thought process.
As for your idea of trading Franzen for Hemsky and Brule. I personally wouldn't think that was a bad trade, but I do think it depends on what Franzen you get. I simply put out that I never thought of Hemsky as a great player. I wouldn't make that trade in Fantasy Hockey either... which take that for whatever worth you want.
I would take him over Hudler... but you have to pay for him too.
Injuries are a concern as well.