As long as they can turn into a dragon they would be eligible, but if they aren't actually turning into dragons then they aren't eligible unless you request a dragon/dragon-shifter AU.

so if a Dragon Miraculous wielder were to turn into a magical dragon instead of a human with dragon-inspired magical armor, that sounds like it would be eligible?)

I'm not super familiar with this canon admittedly, but this would be eligible based on what you've described!