Android 6.0 (Marshmallow) supports USB MIDI, and so does Lemur (versions 5.3.3 and up).
To enable USB MIDI, plug your Android tablet to your computer or MIDI device with a USB cable. Now go into your notifications (swipe down from the top of the screen) and tap the USB connection entry. You'll see the following options:
Now you can select Android USB Peripheral Port as your input/ouput for MIDI Target 0 in Lemur's settings (accessible via the button in the top-right corner of the app).
Note that this does not enable Lemur Editor functionality, or OSC communication. You still need Wi-Fi for those in this scenario.