Ahhh Xeno Gars
Ok off the top of my head there are two ways to do this. One is put the ISO directory information in big endian format. This makes it incompatible with DOS and windows machines. The files you CAN see have BOTH entries in the table. (They have little and big endian tables) so if they have nothing in the little endian DOS/Windows doesn't see anything there. ISO buster will likely tell you if they did that.
Second how big is the disk? IE How much space does the disk volume take. If it's greater than those 2 files.. well it's stil lthere then. SYSTEN.CNF on the playstation is the boot file sort of like the AUTOEXEC.BAT file on a PC. That will likely contain the load information for SLUS_006.64. It sets the stack size and I'm not sure what else.
At this point the Playstation starts the game
Conclusion? I believe the data is in raw sectors. The file information is likely in the EXE file.
However if you find the file names with something like ISOBUSTER, that doesn't mean they didn't do it that way. NOTE if it's loaded as sectors etc. If you find an image file or something on the disk ALWAYS note the location, and compute the sector information. I'm not going to discuse ISO format information to you here. Needless to say it's important in order to find the begining of the file.
Cyb