You'd wait until after the Rule 5 set date, to see if Jimenez was protected or not. If he is protected, you might trade for him. If not, you might wait, unless you think someone else might nab him before your pick.
Yes, Potts and Rosario can pick any team, but if you are willing to trade for players likely to be DFA'd, you probably like them more than others and might offer them the highest contract.