There were a few instances of some of the new enemies and/or variations finding their way to some of the old side missions in the Way of the Demon. I wouldn't expect any mix-ups to the already established ones though, so I would imagine their appearance at the current missions would once again be locked behind the next difficulty level.
Tonfa's were so fucking good in ng2, secret best weapons in that game if you knew what you were doing with them. Dlc might be worth buying just for that if they just lift the mechanics wholesale from ng2.