Similar to the following topic, contacts synced via DavDroid are shown as unknown for SMS in the SMS app.
I also got some contacts synced via my Google account. SMS i get from those contacts or write to those are labeled with the correct name in the SMS app.
My DavDroid version is 1.0.5 and I’m using the Cyanogenmod 13 nightly from 2. April 2016 on my i9195 (Galaxy S4 Mini).