Assuming you’re using the Teensy++ or Teensy++ 2.0 then PlatformIO defines the “teensy-gui” tool as the upload tool (source). This is this tool (source).
I don’t however know if that tools uses the factory programmed DFU bootloader you reference. What upload tool do you use for interacting with this boot loader? Have you tried uploading firmwares with the teensy-gui?