It is the Finnish version of "Wenn die Soldaten". He sings about marching "soldierboys" who are being greeted by handkerchief waving 17-year old blonde girls. Basically making the whole going to war and coming back from it seem like a jolly good time. Video description mentions it is the march song of the Finnish soldiers serving in the Waffen SS Division Wiking, but I cant really say yay or nay to that since I dont know if that is so. However, the reason I chose the song to be the loading music for the map is because to me it reeks of irony.
To explain it in the nutshell, think about the loading song for Seelow Heights. It tells you to ignore and turn away from the war, while that same war is getting closer and closer to home. At the same time the map is really "end of days" feeling. My case is similar: The song sort of glorifies war in its cheerful tone while the map itself is basically hell on earth and complete opposite to what the song is about.