Created an app to convert any folder with audio file to a hydrogen library, basically the app creates a copy of the folder you choose and creates a drumkit.xml with audio entries from your folder. For now you would have to copy this library to .hydrogen/data/drumkits/
You can find it on GitHub here including with details of how it works; the source and the executable.
I created this because I wanted to easyliy import sound samples from other tools I've been using. I hope you enjoy it.