For a more comprehensive answer, you ideally would need to write a somewhat more extensive question. It would be helpful to know what gave you the idea.

The short answer is no, most communists who were in the age-range for military service (17 to 45) would have served in the military. Military service was compulsory in Germany even before the war. Obviously there were some exceptions for men with physical disabilities and those in certain positions, but these applied for all political groups.

Consequentially, one of the most famous communist organisations of post-WW1-Germany was the Roter Frontkämpferbund (~ Red Union of Front-Fighters). Note also that it was precisely the experience of mass-carnage for nationalist causes that brought many former soldiers to the communist cause (and other neighboring ones).