Sorry about that.
Both of the controllers you mentioned require SDL2 libraries to work. The 6 or so controllers we've tested with so far didn't require those, so while we're tweaking other things about the game in the coming two weeks, we'll grab a controller that also requires SDL2 to work and see if we can trouble shoot it. Assuming it's an SDL2 problem and we fix it, then the Saitek P480 should work on Windows but not Ubuntu, and the Dragonrise should probably work on Ubuntu but not Windows. We'll reply to this comment again to let you know if we find anything out.
It was pretty surprising, but that's what the external library we used to assist with controller support says: https://guavaman.com/projects/rewired/docs/SupportedControllers.html (In the chart near the bottom that says "SDL2 Gamepad Support"). It might be that other games are using more robust libraries for controller support.
For now we are still looking into it, and we'll let you know if we find something out. Sorry again those controllers didn't work with the game right off the bat.