What is your sha1sum of the hotmario.chd ?
I managed to softload without changing the sha1 in the hash.
Although working it's indeed a bit of a hassle to get it working.
Found from the runcommand.log that the chd searches a specific name in a specific folder.
If you want a clean roms/cdimono1 roms folder with only hotmario.chd then that file need to be a link of :
/home/pi/RetroPie/BIOS/mame/cdi/hotmario/hotel mario (1994)(philips)(eu).chd
or (not ideal but will work technically)
/home/pi/RetroPie/roms/cdimono1/cdi/hotmario/hotel mario (1994)(philips)(eu).chd
As both paths are added in the runcommand as search paths.
You can also make a dummy file but then the checksum is not correct for scraping gamelists.
Hope you understand this information.