NL pitcher for a large haul of prospects and probably a large contract extension? Sure, nothing can go wrong there.
But seriously, I'd make the deal and take the risk for a talent like Johnson. One thing to bear in mind though, is that Johnson while his young career is off to a nice start, has really only had the one great year, and he's been hurt a few times already. It's not a dealbreaker but it's something to track.