Once the German army was under the control of the Nazis, it is impossible to imagine how citizens, armed with hunting rifles, some pistols, etc. could have put up any significant resistance. Even if they managed to get hold of a machine gun, perhaps a piece of field artillery, it would have been pointless. Once elected, the Nazis had control of the entire army, air force, navy, and all their weaponry, personnel, commanders, organization and would have been very ready to use it- no improvised force could have matched them within their own country.

The general idea has been deeply cherished by the right-to-bear-arms groups in the US for the past 30 years, at least; that the potential resistance of an armed civilian population is an effective counterweight to the power of an armed government. I suspect one of them is the source of this, as I have heard it repeated many times that the "first thing the Nazis did was round up all the guns", with the tacit assumption that confiscation enabled the dictatorship, not the 1933 election. ( disclosure of bias: I myself am a hunter and gun-owner, and have made myself unwelcome at gun shows by posing the embarrassing question of just how effective a few guys with AR-15's in a concrete-block bunker would be against an attack helicopter with mini-guns and missiles. So I may be too ready to assume this is more of the same)

Combined arms tactics don't come into play AT ALL.

Frankly a more armed population in say France would have in all likelihood just made the occupation harsher as reprisals would have been the order of the day from the start as it was for Belgium in WW1, and if your armed forces are willing to go to great lengths then you can eventually beat any population into compliance.

The German Army in particular had a long memory and did not take kindly to partisans taking shots at them as they marched.

This goes back in essence to the Franco-Prussian war, where despite smashing Napoleon III's army at Sedan as the Prussians advanced they would have shots taken at them, and even in their minds held the local pastor's responsible for inciting the violence. These groups had semi official status with the French government, as many had formed from prewar hunting or rifle clubs and were known as " Francs-tireurs" or free shooters.

While they did exact a toll on the Prussians, they also resulted in summary executions when caught and violent outbursts from Prussian troops. And in the end the war was still a crushing defeat for France.

So fast forward now to 1914 and those German troops marching through Belgium and Northern France had grown up with stories from their father's about all this. So as soon as they take a few shots from a village, be it from a true partisan, or maybe a remnant of allied troops, they aren't going to stand for it. Now all of a sudden you have whole villages being burned, with men found to have weapons being shot in the square, and estimates of anywhere up to 7,500 Belgians killed by the middle of 1915 and the German occupation was not appreciably weakened and really the advance was not even slowed except by exhaustion and organized formations of Allied troops.

So no I do not think the evidence support the idea that lack of gun ownership helped German occupation. As you have the Germans again as non mechanized forces (arguably even more vulnerable to partisan warfare due to slower movement speeds) doing just fine and securing major victories despite active threats from partisans in 1870, and perceived threats in 1914.