/tmp/runcommand.log will have information in it after a successful OR unsuccessful rom load. you must be looking in the wrong place. try running a rom that does work and checking for it.
are you reinstalling your system and then doing all this USB drive mapping before you actually get a neogeo game to run? it’s difficult to see where your problems are because you seem to be doing lots of things at once. a fresh retropie install will run a correctly sourced neogeo rom, if it has the right bios installed. there’s no configuration needed.