This is a good point, the team probably will lose a pitcher if another pitcher is signed. Though I'd think it would be the less experienced Hendriks, Albers or Johnson. However if it was Diamond or Worley, the Twins could likely get some kind of return for one of them and DFA'ing them would force interested parties to work out a deal quickly. I'm guessing Hendriks, Albers or Johnson likely would not net a return. I think Deduno is safe from the way they hint a rotation spot is his to lose.
Worley, Diamond and Deduno are out of options. It is the 25 man or DFA. Any trade would be a sell low and the return would be little to nothing. Their lack of option will hurt any potential return.
I believe the others can and will be optioned.