I found out - it worked under uLaunchElf because ule has a more up to date usb_mass driver. I found some newer ones here to replace scummvm's, and now it works.

Is there something special you need to set or a certain file configuration to load games off a usb drive? I have ulaunchelf running off the mem card (modded PS2) and loading scummvm off a usb drive. (Actually a USB SD card reader.) I've tried putting scummvm in the root folder, and in its own /scumm...