Yes, it seems to have been quite common.

Some evidence to back this up is among others Viktor Klemperer's diary who notes in 1941 that the moos among workers is subdued in Germany as can be gauged by them reverting back to using good day when greeting each other instead of the Hitler salute (Victor Klemperer: Tagebücher 1940–1941. 2. Auflage. Aufbau, Berlin 1999, S. 93, 157.)

While not compulsory up until the last years of the Nazi rule, not using it could get you into trouble as can be glanced from the forms when making a report with the Gestapo, where there was a separate field for entering if someone used the greeting or not.

Similarly, the Academy of Sciences examined thousands of private letters and noticed that some 2200 people used the "Heil Hitler" or "Mit deutschen Gruß" at the end of their letters rather than the previously more common "Hochachtungsvoll" (Franz Graf-Stuhlhofer: „Heil Hitler!“ am Schluß von Briefen. Beobachtungen am Schriftverkehr der Wiener Akademie der Wissenschaften. In: Österreich in Geschichte und Literatur 40, 1996, S. 125–128.)

All this points to a rather widespread usage among the civilian population of the Third Reich.