I want to make sure I've got this right, and ain't missing anything.
Running 550 GEN D3 final (far as I can tell), can run the ISO of Little Big Planet with no issues.
I can't, however, play the actual UMD. I get the "can't get game to start" error.
And in neither case (obviously since I can't even start the UMD) can I run the update or get DLC costumes to get added. I can get them ONTO the PSP by connecting and downloading via the PS3. But they don't get recognized as something I can run as an update.
So unless there's a patch I'm missing (or a better CFW which I don't think there is), the only way I can play the full, updated version of the game is to go to the regular 6.20, which I could do via multi-booting.