It is more native than toolkits which try to recreate the controls themselves. But I would not call it "fully native", because it does not let you write cross-platform fully native-feeling apps. It fails at that for the simple reason that that is impossible: different platforms have different UI conventions, including icon appearance, controls with no direct equivalents on other platforms, or with equivalents that have subtle differences in usage, idioms and standard layouts, behavior of keyboard shortcuts and gestures, use of platform-specific features, etc. If you do not spend a significant amount of time tuning your UI for each, you may end up with something that's 80% right, but it will never be 100% right.

Also, wxWidgets has had a lot of problems lately on OS X: high-DPI not being supported properly for years, broken focus, other bugs. It's not just the macros that make it an icky framework, which I say from unfortunate first-hand experience.