TextMesh pro and uGUI currently share one sub forum. However, they are not tied together in reality. You can use uGUI without TextMesh pro and you can use TextMesh pro outside of uGUI. Also, I personally look into uGUI threads but not TextMesh pro threads. Not everybody is using the prefix, so it is sometimes not clear what a thread is about. For both topics are also enough threads to fill a dedicated forum (it feels like 60% TextMesh pro / 40% uGUI threads).