Anyway, one of the reasons I consider that to be a glitch at least to some extent is the fact that you need to do it pixel perfect, and on top of that, depending on the exact frame position of the diggers relative to each other, it may not work. On top of that, bashers or miners on the same spot certianly don't cause one of them to stop.
It sounds like you don't quite grasp
why the digger stops. A digger stops basically when there's nothing more for him to dig. Generally that happens when he's dug through an entire platform. In the trick, you create this situation by having a second digger remove all the pixels underneath the first digger that he would've otherwise dug out himself later in his upcoming stroke. So by the time the first digger do get to his stroke, the pixels are gone, he sees nothing to dig, so he stops and falls. Indeed, if the game does more frequent checks for falling than is currently the case, the truly logical behavior would've been that the first digger falls as soon as the second digger has dug.
You need it pixel perfect only if the first digger is fully on ground, the pixel-perfect position necessary to remove all the pixels underneath the first digger that could cause him to continue digging. If he's digging on the edge of a vertical drop for example, then the second digger has less pixels to remove , and therefore doesn't have to be perfectly on the same spot as the first digger to free him.
There might be some oddness with the behavior under certain timing/frame positions, I'll have to look at the game programming again to see, but in most cases it should work.
As for miners freeing miners and bashers freeing bashers, that can be done too, but not on the exact same spot because you don't remove the correct pixels at that position. I've attached examples for both. The miner one is demonstrated in level Tricky 6, and the basher one in level Mayhem 27. For the basher one, you need 3 bashers because the basher looks ahead a bit further than can be handled in time by just a second basher. Note that the climbers and floaters being assigned have nothing to do with the trick; they just help you identify the lemming that gets freed.