Ottoman Turkey ally Kaiser Wilhelm II had German military stationed in Ottoman Turkey.
[Excerpt] "Dadrian does not accuse Germany of instigating the Armenian genocide; he argues instead that Germany contributed to the genocide through policies that condoned it and that the German government sanctioned German and Turkish officials who participated in the genocide's implementation."
This is a good question that I cannot answer. I have my suspicions but that's all they are.
I’ve never heard of German involvement with Armenia; my understanding is that their advisers were primarily concerned with the Dardanelles.
If scholars end up speculating and are disproven on any point, then a whole denial movement will be born from it.
The book sounds like an effort to shift responsibility away from the Turkish regime that indisputably masterminded and carried out the genocide. The number of German military in Turkey during wwi was pretty small (they had a lot on their plate during that little two and a half front war they were fighting in Europe at the time) and mostly their duties pertained to the efforts to blockade seagoing traffic to and from the Russian Empire. Germany and Austria joined the UK, France, and Russia, and the United States, in the condemnation of the genocide, and did so at the time it was going on. Sounds like the author either has an axe to grind, or wants his fifteen minutes.
https://www.umdearborn.edu/dept/armenian/facts/genocide.html
http://www.genocide1915.org/ogonvittnen_diplomater.html
interesting sidebar:
http://www.worldwar1.com/sfgb.htm