The "Hidden" checkbox in the "Add game" prompt is confusing
I understood afterwards that it was for non-game files such as BIOS files, but the info is kinda buried in the Github Readme page, and I remembered it only because I read about it on the Discord server. I think that since it's not a game, its upload form should not be here.
I suggest to add an "Emulator settings" button somewhere in the emulator's menu itself. For example for PS1 http://gameros.local/platforms/ps1
The "Hidden" option is not necessarily meant for BIOS files. I use it all the time for ROM files. It is meant as a way of managing a larger collection of ROMs. Sometimes you do not want all your games visible in Steam. But instead of deleting and re-adding them, you can simply mark them as "Hidden".