I now have the WeDo crocodile happily chomping on my finger, powered by my Pi, thanks to some help from Alex Bradbury. In order to make this happen you need to add a udev rule which makes the WeDo USB hub readable and writable by the pi user.
Go to directory
/lib/udev/rules.d
make a file called "40-scratch.rules" that contains the following:
ATTRS{idVendor}=="0694", ATTRS{idProduct}=="0003", SUBSYSTEMS=="usb", ACTION=="add", MODE="0666", GROUP="plugdev"
Then start up Scratch, plug in your WeDo USB hub, and the motor control blocks should show up in the Motion area.
Hooray, chomping crocodiles for everyone!
