It took a little digging, but here's the process I followed:
- Locate drumkit audio files and drumkit.xml
- Locate the drumkit name in drumkit.xml
- Create a directory in /Applications/Hydrogen.app/Contents/Resources/data/drumkits using the name found above
- From the directory where the drumkit.xml and audio files are located, execute the following cp * /Applications/Hydrogen.app/Contents/Resources/data/drumkits/GregsKit (but of course, instead of using "GregsKit" use whatever the drumkit name is)
- Restart Hydrogen and find your imported kit in the Sound Library under "System Kits"
- For ease next time, export your kit so that it is formatted properly as an .h2drumkit file
This was much faster than loading each instrument individually. I think it took less time, even with the searching I needed to do to find the location of the system kits. It was worth the hour, and I hope this makes things easier for me or someone else if I ever need to do this again.