I think it would be cool if they both joined. Martha's already been a part of it before, so already knows the team anyway, and Mickey worked for Torchwood in the parallel universe so he'd be used to that sort of work. Plus, he knows Jack, so he'd fit in too.
Then again, although they'd fit in, it could be too much Doctor Who in Torchwood. What I've always admired about the way Torchwood is written is that it could be seperate from Doctor Who, even though they are essentially in the same fictional universe.
I don't think anything has been announced yet, but whatever the decision, I can't say I'll be too bothered either way.