Valve had their own Linux distro and decided to support Ubuntu. There are other Distro's "based off" Ubuntu that would naturally gain support as well. The only serious problems a distro would have is library support. Some Distro's provide libraries in their package installer and some don't. Some make libraries available after a fresh installation, some don't.
So a lot of Linux games bundle the necessary libraries with the game, but this doesn't always work either. Like older games (Unreal 99) have old out-dated libraries that most Distro's no longer support. So you have to manually download and install them.
I use Mint and its based off Ubuntu as well. Mint is more of a legacy compatible distribution. They test and support older kernels/libraries/drivers just to be sure all of your applications and hardware continue to run, even with newer releases.
I know it can be intimidating to support 100's of distributions, but you really don't have to. Just test your game in Ubuntu and chances are it will run in other Distro. In fact, gamers at https://www.reddit.com/r/linux_gaming/ would be happy to help test Fading Light: Descent and offer solutions. There are gamers, enthusiasts and developers roaming that forum and love to help.