Since I have a USB DVD drive and an Nvidia Shield I thought I'd give it a try to see what happens and as I thought it does not work
The shield appears to see the DVD drive but using adb shell I can't see where or even if it's mounted so it's not possible to tell MythTV where the DVD drive is mounted.
Even if you could get the DVD drive mounted I very much doubt it will be able to play encrypted DVD's so like other have said your best bet is to RIP them and make them available over the network.
Some have had some luck with sideloading MLUSB Mounter on to their Shield and using something like Kodi or VLC to play a DVD but the reviews are hit and miss, you have to buy a paid extension and even then it will not play copyright-protected discs.
