I'm hearing conflicting reports on party membership in the Wehrmacht, some sources claim it was forbidden for military men to join a political party as it was seen as a conflict of interest, others claim it was only the higher ups who were forbidden (such as Wilhelm Keitel, Alfred Jodl, etc). A third report I've heard is that one of the two aforementioned options were indeed law but only during in Wiemar Germany, I don't know what happened to it after. I didn't mention the S.S. for obvious reasons (you had to be a Nazi Party member to join). Anyone able to help?
As far as I can tell, from a quick re-reading of Rise and Fall of the Third Reich, party membership in the Reichswehr was forbidden. But by the time Hitler assumed control and expanded the military, this was abandoned. Most of the reading I've come across indicates that most of the Wehrmacht (like the country in general) might have supported the policies of the government without being official members of the Party. I remember reading (and can't recall where) that Party membership never exceeded 10% of the population, so it's reasonable to believe the same was true of the military.
Wilhelm Keitel at his trial claims he was not a member since it was forbidden until 1944 when Hitler allowed it presumably for men of his rank. I too have read things claiming some ideologies of the party may have been supported by Germans but not necessarily enough for them to sign up for a card. I am heard a 10% figure as well although wasn't it for everyone including the military?
I'm not sure about membership for Wehrmacht. It's a good question that I will ask my "source" about. What I did hear was that many Hitler Youth went into the Wehrmacht once they turned 18. In effect, this began to influence the army with Nazi ideology as these junior men rose up through the ranks.
Your "source"? The Hitler Youth were sent to aid the Wehrmacht with some of their missions, one account I'm familiar with is the one by Guy Sajer where the Hitler Youth are sent to help the Gross Deutchland with their first objective after training. He describe ages ranging from perhaps 16-25? Before everyone was deployed, Sajer described the attitudes of some of the Hitler Youth ranging from trying to attack veterans for their defeatist attitudes, showing off, silence, depression, fear, etc over what they should expect, etc. A majority of them were wiped out by the time the battle ended, largely due to inexperince and human mistakes (such as setting of a mine field). The Wehrmacht had a saying on the Eastern Front, "you want to be a hero? The Russians will make you a hero!".