I've never been able to find any info on Spinach either, I would also like to know if it is safe.
I know Vander will eat it ever so often.
I eat baby spinach so I cut up one leaf and gave one to each of them and Vander was the only one who ate it.
Spinach is full of lots of vitamins, unlike lettuce. I feed it to my gliders. It's got lots of calcium in it too. I can't imagine why it would possibly be bad for hedgies(except for the green hedgie thing, lol).