i've been running, meaning hearing, waze through my car play unit since January. I get the police reported ahead warnings and all the guidance but have to run Apple Maps without guidance to see a map on Car Play. So in the following configuration, you end up using both. Don't start Apple Maps and you just get the Waze guidance and alerts over Car Play.
You do have to make some changes in settings though to get this to work. Do so by turning on background app refresh for Waze on your iPhone, location services should be On under privacy, then under location services scroll down to waze and set it to always. Next connect your iPhone to Car Play and open Waze on your iPhone. again, Waze will not display on Car Play. Tap Go Now to your destination in Waze. Waze will speak to you over any Car Play app without closing it. Adjust the Car Play Guidance volume to be louder than the general volume and you're good to go. Will be great to finally get Waze maps on the screen though but this has worked great for me for half a year.