Q:

How do I know which third party dependencies are compatible with Quarkus in native mode? 

In the course of development I may need to add third party dependencies to my project.  In JVM mode it sure works, but how can I identify which dependencies are incompatible with Quarkus native mode? 

A:

As long as your dependency is brought via an extension, then it's usage via the extension is known to work in native mode.  If you directly pull a dependency outside an extension dependency, then Quarkus can't guarantee this.  This does not mean it won't work, just that this cannot be guaranteed. 
The best course of action is to discuss the dependency you want to add with the Quarkus community.  It's possible, someone else it working on an extension for it.