Even if I enable "Omit landfill" it continues to try to place miners magically hovering over lava. It also will place underground belts bridging across lava tiles, which don't work, so some logic would have to be created to route the belts around.

Try enabling the "Avoid placement on water" option, it works the same for lava and oil oceans. It's a little barebones how it places mining drills since it's appropriated from the non mixing ores code.

Ah! Yeah, that does stop it from placing the miners over lava, but it still tries to route belts over it. I imagine that is a tricky problem to solve.