No, it would not backup Contacts. Yes, it would backup Contacts.

*Confused*, eh!

>Yes, it would backup Contacts.

See this question: The author of it was able to backup contacts. It was later revealed that the device on which the backup was performed ran Android 4.1.2. It was a bizarre revelation for me that the backup succeeded. 

>No, it would not backup Contacts.

As per the Manifest mentioned [here]( for default Contacts Provider app in Android versions (in series), for Jelly Bean and above Android versions the ADB backup for Contacts Provider/Storage would be denied by system, and hence your contacts wouldn't be backed up.

It's a mere flag `android:allowBackup="false"` that's the cause of backup denial. See my answers [here]( and [here]( to know more about that flag.