This is odd, the "incident" apparently happened November 2018, came to the school authorities notice in March of this year and is being reported today.
Every report I can find quotes it's source as The Daily Beast, it appears to have been reported nowhere else independently.
The song is not named but is said to be by "Herms Niel" which is not a real name it is the nick name of Ferdinand Friedrich Hermann Nielebock who wrote military music in both wars and in all fairness Neileblock was after 1934 a card carrying Nazi, but most of his music was instrumental with one exception "Das Engellandlied" (song of the Angels) written and published in 1939 with lyrics by Hermann Löns a poet killed in WW one so most definitely not a Nazi. However since the music in the video cuts off after three notes it is impossible to say what they were singing.
If this was a school awards ceremony why was it not dealt with at the time, the video does not appear to be taking place in a school, it is a smallish social room somewhere.
I just have a feeling that though highly distasteful, this behaviour maybe a part of a larger story, or a much lesser one, designed to garner attention and it is not really covert filming it is all very staged.

It will be interesting to see how it develops