[Xoom Q&A, Help & Troubleshooting] Mjammjam:
I did some digging on that. It seems there most of the programs are using the usb-serial-for-android library https://github.com/mik3y/usb-serial-for-android. That library is using the Android USB Host API to access the Usb serial devices, which does not require root - so it is not using the normal linux method of accessing /dev/ttyUSBx.

This usb-serial-for-android library has a USB serial device prober function which tries to find available/compatible devices. Compatibility is evaluated by querying the deviceIDs and comparing them with a static list built into the library (to be more exact, it is only an example list). And my device just is not on the library's list. And I would suspect it is also not on the list of the programs incorporating the library. At least this seems to be true with Droidplanner.

Current list in the library example code https://github.com/mik3y/usb-serial-for-android/blob/master/UsbSerialExamples/res/xml/device_filter.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>
<!-- 0x0403 / 0x6001: FTDI FT232R UART -->
<usb-device vendor-id="1027" product-id="24577" />
<!-- 0x2341 / Arduino -->
<usb-device vendor-id="9025" />
<!-- 0x16C0 / 0x0483: Teensyduino -->
<usb-device vendor-id="5824" product-id="1155" />
<!-- 0x10C4 / 0xEA60: CP210x UART Bridge -->
<usb-device vendor-id="4292" product-id="60000" />
</resources>

current list in droidplanner:

<?xml version="1.0" encoding="utf-8"?>
<resources>
<!-- 0x0403 / 0x6001: FTDI FT232R UART -->
<usb-device vendor-id="1027" product-id="24577" />
<!-- Helibot copied these from FTDI device_fileter.xml file -->
<usb-device vendor-id="1118" product-id="688"></usb-device>
<usb-device vendor-id="1027" product-id="24577" /> <!-- FT232RL -->
<usb-device vendor-id="1027" product-id="24596" /> <!-- FT232H -->
<usb-device vendor-id="1027" product-id="24592" /> <!-- FT2232C/D/HL -->
<usb-device vendor-id="1027" product-id="24593" /> <!-- FT4232HL -->
<usb-device vendor-id="1027" product-id="24597" /> <!-- FT230X -->
<usb-device vendor-id="1412" product-id="45088" /> <!-- REX-USB60F -->
<!-- 0x2341 / 0x0010: APM 2.5 device -->
<usb-device vendor-id="9025" product-id="16" />
<!-- 0x26ac / 0x0010: APM 2.5 device -->
<usb-device vendor-id="9900" product-id="16" />
<!-- 0x16C0 / 0x0483: Teensyduino -->
<usb-device vendor-id="5824" product-id="1155" />
<!-- 0x10C4 / 0xEA60: CP210x UART Bridge -->
<usb-device vendor-id="4292" product-id="60000" />
</resources>

my device id:

[ 1375.613089] usb 2-1: new full speed USB device number 2 using tegra-ehci
[ 1375.875133] usb 2-1: New USB device found, idVendor=0403, idProduct=6001
[ 1375.875215] usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 1375.875336] usb 2-1: Product: FT232R USB UART
[ 1375.875403] usb 2-1: Manufacturer: FTDI
[ 1375.875523] usb 2-1: SerialNumber: A102FKL4
[ 1375.878568] ftdi_sio 2-1:1.0: FTDI USB Serial Device converter detected
[ 1375.878809] usb 2-1: Detected FT232RL
[ 1375.878880] usb 2-1: Number of endpoints 2
[ 1375.878946] usb 2-1: Endpoint 1 MaxPacketSize 64
[ 1375.879066] usb 2-1: Endpoint 2 MaxPacketSize 64
[ 1375.879132] usb 2-1: Setting MaxPacketSize 64
[ 1375.979231] usb 2-1: FTDI USB Serial Device converter now attached to ttyUSB5