NSDAP membership was officially off-limits to all Wehrmacht personal in the 1930s, and party members who joined were suppose to resign their membership.

This restriction was wavered later on and indeed encouraged, however, during the war even many very committed Nazis in the German military did not join the party (i.e Field Marshal Von Model).

I know I"m not giving an answer but I'm posting because I think you are using those statistics to figure out how "Nazified" the German military during WW2 was, and it's not a very good statistic for this question.

Waffen SS (although that's probably 100%...?)

The SS (General and Waffen branches) and the party were two separate organizations and indeed at times, rival organizations and some senior SS figures did not have party membership. According to Mark Mazower there were talks among them for one day displacing the party. So the answer was not 100% but unlike the Heer most of their senior officers were party members.