If the off-duty is in his jurisdiction and its a violation, the other officer can sign and the off-duty can file a supporting deposition. It would be easier tho for the off-duty to sign. If it's a misdemeanor (reckless driving usually is) then it doesn't matter, any officer can make that arrest or sign a statement supporting that arrest anywhere in the state. At least in NY, and most states are similar as far as procedure.