Nope, can't play the games with splitted files from external hard drive.
Yes - you'll need to copy them to internal one.
It has a little to do with Open (or any other for that matter) manager - PS3 simply has NO native suppport for NTFS hard drives and on top of it even if someone would try to code support for it it woudl be not as easy plus it's not exactly the best file system to choose - there is more file systems out there than just FAT32 and NTFS
This basically allows you to store your 4GB + file games on your external when your not playing them. When you're ready to play one of them, swap it to the internal and play it. This is useful for people out there with small internal HDDs, since you can easily move your games to/from internal. Combine this with the PS3 Game Ripper to rip unnecessary videos, and you can effectively manage your space.
Open Backup Manager has this feature built-in, but its nice to manage things from a PC also.
This is an excellent temporary solution until we can use a different filesystem on external drives.
Oh, didn't know that Comgenie's splitter is compatible (filesize and extension). I tried his file manager on my ps3 and it has copied stuff much slower than Open Manager. Perhaps that is why I didn't use his other creations...
But what about the cryptography and reverse engineering ? Aren't there books online about that ? I would do it but I don't wanna get sued. Plus I don't know how to program/re any way's I'm about to study CS at my local college.