Crabs (and shrimp) will be lunch, except for hermits...lionfish pay no attention to them or snails.
You could keep small scorps, and even larger waspfish with your fuzzy if you want to stay with that theme. Otherwise, you'll want to avoid small torpedo-shaped fish, as they're quite consumable.
Medium-sized wrasses such as Halochores sp. should be fine. We've also kept larger anthias with dwarf lions...our trio of O. borbonius did really well with them. Some of the smaller hawkfish species would also be OK.
Depending on your tank size, you could also keep another dwarf lion species (fu manchu, Green/Hawaiian, zebra), or even pair your fish up. Your fish looks a bit young, but I suspect that it's a female.
Here's a little vid of our 100 gal lionfish lair (we had just moved the fu into the tank, so it was sulking):
http://www.youtube.com/watch?v=k9qDwbH2uNk