There are two things that need to be considered here:

1.) Service in the Wehrmacht and party membership

Up until 1944, while serving in the military, party membership was put on hold. That and the fact that the Wehrmacht was an army reliant on drafting people makes it really hard to gauge how many members of the military were also members of the Nazi party. The best estimate is that party membership in the army reflects party membership in the general population, so between 7 and 8 percent depending on the time.

An approximate answer to your question can only be given for certain groups within the different branches. Support for the NSDAP and memebership were especially high among doctors and to slightly lesser degree jurists, especially judges. I have not found info on the doctors in the Wehrmacht but for judges, Kerstin Theis proved that 69% of all military judges were members o the party.

It is also fair to assume that despite especially the Luftwaffe - as the youngest branch and the one run by a Nazi official Göring - attracting many Nazis, that the Heer had the highest number of NSDAP members among its ranks just due to the fact that it had the highest number of members.

2.) Being a Nazi is not contingent on being a member of the party

Depsite membership to the Nazi party being put on hold when on active duty, the support for Nazi aims and policies on a practical and ideological level was high among the Wehrmacht.

To adopt form an earlier answer rhere:

The Wehrmacht had about 18,2 Million active members from 1935 to 1945 and it is impossible to estimate just how many were involved in war crimes. It can be said that the entire leadership of it was complicite through making policy but when we get to the lower ranks, it is impossible to determine, especially in light of the question what exactly constitutes complicity.

The Wehrmacht was an institution in which most members did not serve completely voluntary. Rather they were drafted and of course within the army itself there was a considerable degree of social pressure to do as your fellow soldiers did. It is a fair estimate that the vast majority of Wehrmacht members, especially those who at one point served in the Soviet Union and the Balkans were aware that crimes were being committed. It is also a fair estimate that a considerable number of those who at one point served in the Soviet Union or the Balkans (especially the later) were involved in some form of crime, i.e. were present during its committal, pulled the trigger, guarded victims etc. However, in a strictly legal sense not all of these were complicit in these crimes. In a historical sense, one can say that they were though and also in a certain moral sense.

That doesn't mean that every member of the Wehrmacht, especially those serving as rank and file soldiers were "evil" but it does mean that they were - with different degrees of voluntariness - members of an organization that was fully complicit in crimes as well as murderous on its own.

Sources:

• Wolfgang Benz (Hrsg.): Wie wurde man Parteigenosse? Die NSDAP und ihre Mitglieder. Fischer, Frankfurt am Main 2009.

• Evans, R. J. (2005). The Third Reich in Power 1933–1939.

• Bartov, Omer (1991). Hitler’s Army: Soldiers, Nazis, and War in the Third Reich. Oxford University Press.

• Christian Hartmann, Johannes Hürter, Ulrike Jureit (Hrsg.): Verbrechen der Wehrmacht. Bilanz einer Debatte. München 2005.