It was the (secret) investigation into the cooperation between the NSA and FE which was named "Dunhammer", not the cooperation itself, according to this report by DR (https://www.dr.dk/nyheder/indland/forsvarets-efterretningstj...)

In other words, "Dunhammer" revealed the cooperation. A far more serious allegation, in my opinion, is that FE allowed NSA spying against Danish citizens. An allegation which (again, in my opinion) warrants a charge of treason.