There are two unofficial Spine runtimes for Haxe, NMESpine and spinehx. Unfortunately, they're both pretty out of date at this point. Instead of trying to catch them up, I created a new one, using the current official AS3/libgdx runtimes as a reference:
https://github.com/bendmorris/spinehaxe
Spinehaxe is pure Haxe and isn't dependent on any external libraries.
I also have a renderer for OpenFL/HaxePunk, which includes a HaxePunk Graphic that renders animations and tracks hitboxes of slots:
https://github.com/bendmorris/SpinePunk
Feel free to use or contribute!