- Modern Germans don't really see themselves as descendants of those Germans, in the German language both are named differently. Modern Germans are 'Deutsche' - ancient Germans are 'Germanen'. English does not make this distinction. There are more annoying confusions like this, for example, the Germanic tribe of the Saxons has nothing to do with the modern state of Saxony, as the ancestors of modern Saxons spoke a different dialect. There are several breaks like this in between modern Germany and Germanic tribes which are masked by nomenclature.
- German (Deutsche) Catholics distanced themselves from the 'barbaric', non-Christian Germanic tribes.
- As usual, the Nazis ruined it. The battle was sometimes used for propaganda reasons by the Nazis, replacing Romans with Jews. Modern Nazis are also using it for their own purposes (replacing Romans with immigrants and the US)
Edit: the battle itself isn't silenced or anything, I do remember quite a few events when the 2000 year anniversary happened, including the cover of the SPIEGEL having it (IIRC?)
People who want to identify with victory over Romans to fuel a nationalistic mindset won't stop at Arminius, they also claim the legacy of various gothic etc tribes who troubled and/or continued thedying western empire.
If you look at central Europe in the last 2000 year it isn't surprising I think, most of the time it looks like a giant disaster.
Also German TV is full of historic documentaries about that time - at lest the public service broadcasters (phoenix, zdf info, arte, etc). Of course you will not notice that if you only follow the private channels.
However I would guess, that your colleagues just forgot about the 'Schlacht im Teuteborger Wald', because it definitely visit part of the history curriculum.
In modern days the French Revolution as a well as Bismarcks doing have the focus for the 'identity' of Germany.