Yes, they can. It's presence or absence on your credit report has nothing to do with the legal options available to the creditor.
Yes, provided the debt is not beyond the statute of limitations in your state for legal action. If the debt is beyond the SOL, the debt is time barred for legal action to collect. They can still take you to court and if you don't show up, they win by default even if the debt was beyond the statute of limitations.
They sure can.