Not directly I suppose. Right now on a Mac I have set up Zoiper to use the Mac OSX Contacts app, and the address book is exclusively writing and reading from a CardDAV account. So it kind of works.
The current downside of this is that I cannot edit my contacts in Zoiper, I have to edit them in the Mac Contacts app instead (or whereever I can edit a CardDAV contact). But it's a start for me.
Since things like Nextcloud are becoming more and more widely used and CardDAV support is becoming better on all the platforms I use (Mac, Ubuntu, Win), I have asked the Zoiper Sales about this. They answered pretty fast :-)
"Thank you for contacting Zoiper.
CardDav support is included into DEV plans already. Unfortunately we can't provide a time frame for implementation.
Dimitar - ZoiPer Team"