Minetest has no native gamepad support, but even on Android there will be keyboard & mouse support. To use a controller you'd map your controller buttons to the appropriate keyboard/mouse keys (not to the touch screen). I've done this on a Linux handheld with a touchscreen & it works great. I wind up using "hybrid controls", where for some crafting-related things I use the touch screen & everything else I use the gamepad.
If you go this route you'll a keymapping software for Android. I don't know of one unfortunately, but here's a thread discussing options.