Dernbach does appear to be in the Kingdom Of Bavaria. However, it is not impossible that, if he did serve in the military, he might have joined a neighboring kingdom's army.
See the attached link that shows Germany's overseas possessions. As you will see, their overseas empire gets going in 1884. European powers carved Africa up at this time in what was called the 'scramble for Africa' and formalised by the Berlin conference of 1884-5. It is thought that Germany ended up with the less valuable, more difficult to control areas because they were late-comers to the 'party'.
I am not too knowledgable on foreign deployments in the German colonies, but my impression is that most, probably all, of the local security was provided by locally recruited soldiers, with a relatively small number of German soldiers providing the officer corps, and perhaps also non-commissioned officers. These forces reported to the colonial authority rather than individual German kingdoms. You will need to do some research yourself to fill out the blanks here.
Prior to 1884 German involvement in Africa was limited to a few trading stations.http://en.wikipedia.org/wiki/List_of_former_German_colonies