Unfortunately there is no additional documentation related to Linux.
Previous version of ZSTAR the initial one (not the ZSTAR2) was able to compile on Linux but ZSTAR3 unfortunately not.
There is nor any API that interfaces the Linux or Android OS with the ZSTAR3 (or any ZigBee solution device). Therefore, you will have to develop it by your own. Please refer to the ZSTAR3 reference manual – chapter 5 about the software design to get familiar with the ZSTAR3 RF protocol and packet format. This will definitely help you to build your API. You can also use another USB dongle if you do not want to use the ZSTAR3. There is a USB dongle reference design for the MC1321x available on Freescale website. Also, there is a USB dongle board using the ARM-based MC1322x device. However, if you just want a simple network such as the one used in ZSTAR (SMAC), you should definitely use that hardware or the MC1321x (HCS08 core). Regarding to the USB stick drivers for Linux, the ZSTAR is standard USB CDC class and it should work in Linux with the standard driver preinstalled. Please refer to the i.MX51 EVK Linux Reference manual – chapter 30 about the ARC USB driver for more information about the USB driver. At the end of the day, you will be able to plug the USB stick and be ready to use. Then you can implement your API with the information stated in the ZSTAR3 reference manual. You can also use another USB dongle (1321x for example) and load a wireless UART application to it so anything you send it via serial interface, will be transmitted over the air.