Unlike the individual slave mode serial adaptor chips an Android Accessory is a higher level abstraction of a device. It is presented as an input stream and an output stream and it is up to the application program to detect and control whatever is at the far end of the Accessory.
I have seen FT311UARTInterface.java and it appears there is nothing in there that cannot be implemented by the standard USB library, or even through the streams of a UsbSerial Accessory as long as you don't need to detect things like Manufacturer, Model, Version etc.
The UART config data appears to be an 8 bye packet sent through the normal output stream. It is, however, a mystery to me how the chip identifies this as config data and not data data. It is also of interest that it seems to avoid sending a data packet of exactly 64 bytes, instead sending it as 63 bytes and then one byte. Very odd, particularly as there is further processing after the stream so there is no guarantee that the data will be sent in one single USB data transfer anyway.