Like DaMummy said, I'm sure all the games you will find come now in a files&folders format, not an ISO.
so, as long as no files are bigger than 4GB, you can put and play the game on external HDD.
If one of the file is bigger than 4GB, you can put the game on FAT32 HDD, but you have to transfer the game to the internal HDD in order to play.
When you rip or transfer a game to external HDD and a file is bigger than 4GB (for example star ocean has a big 25GB file), it will be splitted in many 4GB files, with the extension renamed to .ext.666xx, where xx is an incremental value.
the folder name will usually be renamed with an underscore : BLESxxxxx (not splitted) -> _BLESxxxxx (splitted, has to be copied to internal HDD)
A) If you download a game with big files not yet splitted, you have tow choices to put the game to internal HDD :
1. use an FTP server on PS3 (either Blackb0x ftp 1.1, or Gaia Manager internal FTP), and connect to the PS3 with an FTP client on your computer. (use an ethernet connection!)
2. use a splitter software first, to create the 4GB files with the correct naming. There are 2 software doing that job.
OpenSplit1.2 (a java application), and the second one is
PS3Splitter
launch openSplit, select the BLESxxx folder, and it will convert all the big files in all folders recursively, and rename the processed folder to _BLESxxxxx
B) If you download a game with underscore in the name, don't use FTP to transfer the game, or rebuild the big file first. (It's totally logical, but I guess I had to mention it, just in case
)