That's one problem that we have to figure out, actually. In LieroX, you dig by hitting the direction opposite to the direction you are holding. For example, if you are holding right, you just tap left to dig. This isn't possible with the dpad, so we need to come up with some fix for that.
Nah, Circle Pads are the best. Besides, you would need 2 thumbs on it to handle it well like that, and then you wouldn't be able to do all the other things in LieroX. ;P Maybe some Outer ring that could be used as an additional means of input. For example, you could be holding right and rotate the outer ring a little to mean tap left.