No; gnss-share is not something apps should ever be using. They actually can’t use it even if they try because of missing permissions.
gnss-share is used by Geoclue, and that’s the service that’s actually used by applications. Writing a Geoclue backend for Navit would be a better idea.
gpsd being a system service can access gnss-share just like Geoclue does, so that works too. You just need to be aware of all the consequences of exposing your GPS data via gpsd (access control etc.)