TLF renders Arabic text correctly no matter where it comes from as long as you feed it UTF-8 encoded text.
Regarding the mirrored components, it's planned for Gumbo but I think Adobe didn't yet start implementing this feature. So it wouldn't help to migrate to Gumbo for now.
I advise to use TLF for text and implement the component mirroring manually on a case by case basis. Especially for complex components like the tree control, you can see for example if you really need the folding functionality and if not, you could implement your own 'simple' mirrored tree.
This article could be helpful:
http://corlan.org/2009/01/19/how-to-use-text-layout-framework-in-flex-32-or-air-15/
If you need help, please don't hesitate to contact me directly.